A Very Expensive Poison: The Definitive Story of the Murder of Litvinenko and Russia's War with the West

8 An Inspector Calls ^{Moscow, December 2006}

In early December, nine Scotland Yard detectives flew to Moscow. The weather when they landed was noticeably colder than in London – a sharpness that pricked the lungs. The sky was a forbidding grey. British embassy staff met them at Domodedovo Airport. The press was there too: TV cameras, lots of them, and noisy reporters. Litvinenko’s murder was front-page news around the world. The men from the Met declined to comment.

They were driven north towards the centre of Moscow, along a forest of silver birch trees bent under snow. The route passes Gorky Leninsky, an official sanatorium used by Lenin, and rows of wooden dachas. Once you are inside the capital’s orbital motorway the landscape grows urban: there are depressing ranks of dull tower blocks and the blue domes of a neo-Byzantine church. Then, in the centre, a giant titanium statue of Yuri Gagarin and the Moskva river, already white and encrusted with plates of ice.

The British embassy is a modern building on Smolenskaya embankment; new diplomatic flats overlook the river. Here the visitors got security passes and a temporary office. Outside is a bronze statue of the great sleuth Sherlock Holmes and Dr Watson; Sir Arthur Conan Doyle has many fans in Russia. Poems by British and Russian authors are displayed on stone tablets in the embassy wall.

Even before Litvinenko’s killing relations between the UK and Russia were sticky. They were about to get a lot stickier.

Scotland Yard’s mission was diplomatically sensitive. The detectives’ main task was to interview Lugovoi and Kovtun and to collect as much evidence from Moscow as possible. At this point, the two Russians were officially witnesses, not suspects. But the detectives knew Kovtun and Lugovoi were in the frame for murder. This was an unprecedented international inquiry. Seemingly the trail led back to the Russian state itself.

The Kremlin had promised to ‘actively assist’ the UK government in its inquiries. The Russian prosecutor general’s office offered ‘full support’. It even hailed the ‘constructive and dynamically developing cooperation’ between law-enforcement agencies in both countries.

At the same time, senior Russian politicians from Putin downwards had noisily denounced Litvinenko as a nobody and ‘third-rate small fry’ – in short, as someone not worth murdering. Sergey Ivanov, a spokesman for Russia’s foreign-intelligence agency, claimed his service hadn’t assassinated anybody since 1959 and the operation to kill the Ukrainian nationalist leader Stepan Bandera. Why start now? The police should turn their attention, Ivanov suggested, to Litvinenko’s entourage in London.

Others suggested that Litvinenko had it coming. During a debate in the Duma a day after his death, deputy Sergei Abeltsev said: ‘The traitor received the punishment he deserved. I am confident that this terrible death will be a serious warning to traitors of all colours, wherever they are located. In Russia, they do not pardon treachery.’

Abeltsev was a member of the ultra-nationalist Liberal Democratic party. Its leader Vladimir Zhirinovsky, a clever clown licensed by the Kremlin to send out politically useful messages, called Litvinenko a ‘scoundrel’. MI6 killed him, Zhirinovsky said. Gennady Gudkov, a Duma deputy and ex-FSB colonel, accused Berezovsky. Nikolai Kovalyov, the former FSB chief, observed that high-profile defectors to the west like Gordievsky (in Britain) and Oleg Kalugin (in the US) still enjoyed ‘good health’. No one had murdered them.

Then there was the polonium. Senior figures argued that the use of polonium demonstrated that Moscow had nothing to do with his death. As Sergei Lavrov, Russia’s foreign minister, put it, why make a spectacle? Lavrov told the Trud newspaper: ‘Why would the intelligence services spend millions [on polonium] in order to send to kingdom come a former rank-and-file agent, whose absurd accusations against them have long ceased to be taken seriously?’

These statements made a kind of sense – if the aim of Litvinenko’s murder was to make a spectacle. They were less persuasive if Litvinenko’s assassins – and those in Moscow who sent them – had assumed the poison used to murder him would never be found. These were early days. But to the inspectors – now encamped in the Radisson Hotel, overlooking Europe Square and the frozen Moskva, from where cruise boats depart in summer – this seemed the most likely version.

The British police force is an egalitarian organisation, with a fine disregard for rank when it suits. The team in Moscow included senior officers from the Yard’s SO15 counter-terrorism unit: Chief Superintendent Timothy White and Inspector Brian Tarpey. White dealt with the embassy and the Russian authorities; Tarpey was in charge of day-to-day operations. There were three Russian-speaking constables. The investigators took with them standard police equipment: recording devices, tapes, notebooks.

The next morning, 5 December, they headed to the Russian prosecutor’s office. The building in Tekhnichesky Lane is in the same part of town as Lefortovo Prison, the FSB pre-detention and investigation centre where Litvinenko spent eight months in jail. The area on the east side was once Moscow’s foreigners’ quarter. The young Peter the Great held all-night drinking parties there with his Swiss mercenary friend and mentor Franz Lefort.

Waiting in the prosecutor’s office was a high-level Russian delegation. It included Russia’s deputy chief prosecutor Alexander Bastrykin, later promoted to head the investigative committee. He was one of the men linked to the Russian mafia in Spain by Grinda, the Spanish special prosecutor for corruption and organised crime. It also included senior investigators, the head of the legal assistance division, and other specialists. Twelve people in all.

This, surely, was a good sign?

The detectives, however, soon found that the Russian authorities intended to manage all parts of the investigation. Bastrykin announced a series of rules. Scotland Yard wouldn’t be allowed to question witnesses directly. Russian officials would do that. The British side could submit questions – in writing and in advance. Scotland Yard’s tape equipment wasn’t needed; only the Russian side would be permitted to carry out audio recordings. ‘I found that a little bit strange,’ Tarpey said.

This initial meeting set the tone for what followed. Over the next two weeks the Scotland Yard team found itself in a bizarre and sometimes ridiculous bureaucratic pantomime. ‘We were very obviously being railroaded into a situation where we had little or no control,’ Tarpey said. He reluctantly agreed to the prosecutor’s conditions. The Kremlin’s apparent goal was to give the impression of cooperation – while sabotaging the investigation where necessary.

Moscow was insisting that Lugovoi and Kovtun, Litvinenko’s assassins, were actually victims. In reality, both men were fine; they, after all, hadn’t ingested radioactive polonium. The Russian authorities claimed that their condition was ‘rapidly deteriorating’. This might be the only opportunity to talk to them.

Kovtun was being ‘treated’ in Hospital No. 6, a Moscow state clinic. The clinic was named after a USSR deputy health minister, Avetik Burnazyan, who helped to develop the Soviet atomic bomb. It specialised in radiation victims. Some of those affected by the Chernobyl disaster were sent there. The building – a Lego-like seven-storey block – is in the capital’s Shchukino district, on a street of Khrushchev-era apartments and lime trees. Nearby is a wooded park with a lake and natural spring, from where pensioners fill plastic water bottles; this would shortly become my Moscow jogging route.

The detectives set off for the hospital, following a lead Russian vehicle. It drove at high speed – and then seemingly got lost. Tarpey was informed that only one of his officers – Russian-speaking constable Oliver Gadny – would be allowed to see Kovtun. After two hours in heavy traffic they arrived at the federal clinic. It was 8.45 p.m. The official in charge, Vadim Yalovitsky, said that under Russian law a witness couldn’t be questioned after 10 p.m.

Gadny was ushered inside. He met the hospital’s chief doctor, Konstantin Kotenko, who appeared nervous, and discussed with the Russian investigator Alexander Otvodov the list of questions. The mood between the sides was ‘cold and suspicious’, Gadny said. The constable donned a protective suit. He was escorted into cabinet number eight.

There was Kovtun – dressed in cream-coloured pyjamas and wearing a paper face-mask and a blue plastic head covering.

Kovtun seemed tired but not visibly ill. Kovtun’s hair might have been shaved off but it was difficult to tell, Gadny thought. He had dark rings under both eyes, two bags under the right, one under the left. He was almost blind in the right one – an injury going back to a brawl with Russians, according to his ex-wife. His breathing was normal. In his notebook, Gadny wrote: ‘KOVTUN was a white male, with (yellow) tanned skin; aged mid thirties; with brown eyes, full brown eyebrows and full eyelashes.’ And: ‘He had a 5 mm round pock-like scar on the right side of the bridge of his nose.’

It seemed Kovtun was unperturbed by the accusations against him. He offered a ‘look of resignation bordering on boredom, particularly when being addressed by the Russian prosecutor,’ Gadny said.

Otvodov asked the questions in a rapid, stern manner, speaking clearly and loudly.

Kovtun described seeing Litvinenko in the Millennium and said that he and Lugovoi were with him ‘for half an hour’. On first meeting they had hugged, as is the Russian custom. After leaving the bar, they chatted for eight minutes near the hotel entrance, Kovtun said. Litvinenko’s poisoning was a mystery, he added.

After ten minutes, the chief doctor announced the interview had to end imminently. Gadny protested and was allowed to ask a couple of questions. Then:

And that was that. The party left and went down a corridor to a small conference room. There they were tested for alpha radiation. An older doctor waved a scope – a kitchen-roll-sized tube with a flat circular plate – over Gadny’s skin. The detector made an irregular high-pitched beep. There was no contamination. The constable left the hospital. It was dark. He rejoined his colleagues, who had been waiting in the car park. Back at the embassy, he photocopied his notes and put them in a tamper-proof evidence bag.

The interview had lasted a mere thirteen minutes. From the 118 questions submitted to Russian prosecutors Kovtun answered eighteen.

Meanwhile, Scotland Yard’s attempts to meet Lugovoi were going nowhere. The next morning, 6 December, the team arrived outside the prosecutor’s office. Staff allowed only one person inside – Detective Superintendent Alan Slater – taking him on an odd circuitous tour of the building. Inside, officials berated Slater about SO15’s alleged failings. The complaints concerned minor administrative details; Slater felt them overblown. ‘I think I’d been summoned there just to be told off,’ he said.

The sergeant asked when he might talk to Lugovoi. The reply: you can talk to him for one hour, when doctors permit.

That evening in London, the press office of New Scotland Yard announced that Litvinenko’s death was being now treated as a murder inquiry. The news went down badly in Moscow. Detectives had been due to interview Lugovoi on 7 December. The interview was cancelled, rescheduled and cancelled again. Russia announced its own criminal inquiry into Kovtun’s ‘poisoning’ – a counter-move. There were further delays, and a meeting in which Russian prosecutors claimed that Litvinenko had aided Berezovsky’s ‘bogus’ claim for UK asylum.

In Britain – actually on sabbatical in Oxford, learning Russian ahead of my Guardian posting to Moscow – I received an email from British Airways.

It said:

The email went on to say that initial tests revealed ‘very low traces of a radioactive substance’ on board two of the planes. It said the UK’s Health Protection Agency had concluded there was no risk to passengers from one of them, and that ‘monitoring is continuing on the second aircraft’. BA listed the affected planes on its website. It gave the number of an NHS Direct helpline.

I checked BA’s website: my wife Phoebe and I had flown on a polonium plane. I called NHS Direct. The helpline wasn’t terribly enlightening – it gave general information and suggested that if concerned I should go and see my doctor. I hung up. After all, I was feeling fine.

Behind the scenes, the British authorities were trying to identify all of the aircraft used by Lugovoi and Kovtun in their journeys to and from the UK. In addition to their BA flights, they had travelled on 16 October from Moscow to London with Russian carrier Transaero. They sat in seats 16F and 16E on the outward leg, and in 26F and 26E on the return trip two days later. The police identified the Boeing 737 planes involved, EI-DDK and EI-DNM.

The UK Foreign Office asked the Russian authorities for help. It suggested that, given the potential risk to public health, they test both aircraft for radioactive contamination. The reply was prompt. Russia’s chief public health minister Gennady Onishchenko told the British embassy in Moscow that extensive checks had been carried out. He was happy to announce that no radiation had been found on either plane.

Despite these reassurances, teams from the Atomic Weapons Establishment were made ready. Scotland Yard wanted to examine the aircraft for evidence. In early December, experts tested the second Transaero plane, EI-DNM, after it landed at Heathrow. To their surprise they found low-level traces of polonium – eight becquerels per centimetre squared. Onishchenko’s remarks – widely reported in the Russian press – were a lie.

The results were passed to COBRA, the UK government’s emergency response committee. A request was sent to the Russian foreign ministry asking for permission to test the first Moscow–London plane. This was likely to show higher levels of contamination, since the polonium had originated in Russia. The plane never arrived. It appears the Kremlin instructed Transaero to cancel the flight. EI-DDK never came back to UK airspace.

As for BA 873 – the plane used by Lugovoi and his family to fly to London on 31 October – polonium was found here too. The highest readings came from Lugovoi’s seat, 23D. Contamination was discovered on the BA aircraft in which they flew back to Moscow on 3 December, especially in seat 16D. The very expensive poison had left a very detectable signature.

Back in Moscow, British detectives were finally granted an audience with the man himself, again in Hospital No. 6. DI Slater travelled with Otvodov in a van with blacked-out windows, its blue lights flashing. They arrived, entered via a rear entrance, and went up the stairs to a room with a table.

Lugovoi was dressed in a hospital gown, as befits a patient receiving medical treatment. Underneath, Slater noticed with surprise, Lugovoi was wearing an expensive designer T-shirt, black with a white motif. The gown, it appeared, was for dramatic purposes.

Doctors had claimed Lugovoi was gravely ill. To Slater, he looked positively fit and healthy – and appeared to have been driven to the clinic from outside. Slater had instructions to check Lugovoi’s eyebrows and arms; if he’d been suffering from radiation sickness his hair would have fallen out. He had a full head of hair.

Lugovoi’s interview lasted longer than Kovtun’s and he gave better answers. He talked about his family – he was estranged from one of his daughters, Anastasia, who lived in the city of Kursk. He spoke of his business activities – his factory in Ryazan province which made kvas, beer and wine. And he gave an account of his three trips to London in October and November, including his dealings with Litvinenko.

According to Lugovoi, he and Kovtun had arrived back at the Millennium Hotel at 4 p.m. We know this is untrue: CCTV footage shows them arriving half an hour earlier, with Lugovoi and Kovtun both making separate visits to the gents’ toilets, later found to be heavily contaminated with polonium. ‘We didn’t go upstairs but went straight to the bar to wait,’ he said. ‘About ten minutes later, Litvinenko arrived in the lobby and I invited him to sit.’

Litvinenko spoke mostly to Kovtun about Hamburg, Lugovoi said. The meeting broke up, he added, when his daughter Tatiana appeared at the entrance to the Pine Bar and his son Igor came in: ‘I introduced him to Litvinenko. Maybe they shook hands.’ Lugovoi said he’d known Kovtun for thirty years, and that Kovtun lived in Moscow.

After one and a half hours, a doctor told Slater the interview was over. The detective hadn’t finished. Nevertheless, Lugovoi got up and left, telling Slater breezily in English:

‘Goodbye, see you later.’

The encounter had yielded some useful information. It confirmed Lugovoi’s movements in the UK, and gave a sharper picture of his contacts and associates. But many questions were unanswered. Slater drew up a list. Among them: ‘Clarify Millennium meeting. Who sat where at the table? Can you draw a sketch plan? How was the meeting arranged? What telephones were used?’

The next day, Slater returned to the prosecutor’s office to agree a transcript of the Lugovoi interview. He’d taken notes and typed them up. Otvodov produced the official Russian version of the meeting. Some of what Lugovoi said was missing. It had been edited from the protocol.

It appeared that the Kremlin wanted to remove all references to the Russian mafia in Spain and its links with Russian politicians. Lugovoi’s account of his conversations with Litvinenko about Spain had disappeared. Litvinenko had described how he had helped arrest Zakhar Kalashov, known as Shakro, a leading Russian mafia boss. He had also told Lugovoi about ‘Jorge’, his contact in Spanish intelligence.

The omission was significant. Lugovoi had mentioned Spain before Litvinenko’s work for the Spanish security services had become public knowledge. It meant that the Kremlin knew Litvinenko was investigating an organised crime syndicate linked to Putin and to corruption at the top of Russian power. It also knew that Litvinenko was a key witness in a future possible trial.

The now-vanished passage quoted Lugovoi as saying: ‘Litvinenko knew I wanted to go to Spain and we discussed it. He said he had a friend in Spain. Litvinenko told me that Russian criminal elements were buying property in Spain. On the 26th and 27th [October], Jorge called Litvinenko and Jorge speaks Russian. Litvinenko told me that Shakro, a criminal, was arrested in Russia, the same kind of operation is going to be done in Spain. It’s connected with money-laundering.’ Litvinenko had said the sums involved were large – $250 million.

Slater raised the missing section with Russian officials. They brushed away his concerns. Slater reluctantly signed and added a dissenting note saying the protocol was incomplete.

During the second week in Moscow, the detectives got access to other witnesses. They included Lugovoi’s wife, Svetlana; Sokolenko, the third man at the Millennium Hotel; Lugovoi’s personal assistant Angelina Idrisova; his lawyer and doctor.

Svetlana Lugovaya’s interview took place at the prosecutor’s office. Her answers were curt.

Under the surface, the Lugovois’ marriage looked to be in trouble. What, if anything, did Svetlana suspect? She and her children had all been exposed to polonium and were treated at a private hospital; little Igor had shaken Litvinenko’s hand. Her husband had put their entire family in peril. What kind of monster would do that? Lugovoya would later divorce her husband. In April 2013, aged forty-six, Lugovoi married again, to a 23-year-old named Ksenia; two years later they had a son.

Sokolenko, meanwhile, said he’d flown to London to attend the CSKA Moscow–Arsenal match. His trip had been touristic, he said. It included beers with other fans who’d flown in from Austria, a bus trip, and a visit to Madame Tussauds. He went shopping with Lugovoi and Kovtun. They visited a toyshop, where Lugovoi bought cartridges for a computer game as a present for Igor. Sokolenko purchased teddy bears. He said he knew nothing about polonium.

By 19 December, the detectives had wrapped up. All that remained was for them to collect the interview tapes from their Russian counterparts. Tarpey went to the prosecutor general’s office. He was surprised to find, for once, no media outside. An official escorted him to a third-floor room. Inside he saw an array of reporters from Russian state TV.

Tarpey said he was ‘totally unprepared’ for cameras and would have objected, given a chance. Russian officials insisted he make a small speech, thanking the Russian prosecutor for his help and assistance. Tarpey muttered a few polite words. He was taken to a table, where officials presented him with lever-arch file binders containing the interview tapes. The cameras whirred and clicked; Tarpey signed a receipt.

It was a nice little piece of television and proof, surely, that Moscow was as keen as London to uncover the truth? For much of the mission, the Kremlin had led Scotland Yard investigators by the nose. It had been a difficult, high-profile trip in which officers had found themselves uncomfortably under the media’s glare. Their task was to collect evidence and often this hadn’t been possible.

Still, Tarpey thought, at least he had the audio-recordings.

When the detectives got back to Scotland Yard they found one final unpleasant surprise. Seven of the tapes were fine. But when they played the eighth, the recording of the interview with Lugovoi, no sound came out. The tape was blank.

From his fifth-floor office, Thomas Menzel had an impressive view of Hamburg. The city’s police headquarters were located in the green suburb of Alsterdorf. The detectives who worked there nicknamed the HQ ‘Polizei-Stern’ or Police Star because of its unusual ten-sided design. Through his large corner window, Menzel could see a light athletics track stadium, cranes, a line of trees and a police training building immediately below him.

Menzel was aware of Litvinenko’s case from the German press. It was, he thought, an extraordinary business – reminiscent of the Cold War, and involving a substance he had never come across before in many previous murder inquiries. Menzel was the head of the criminal investigation department in Hamburg’s Kriminalamt and the director of its organised crime unit. His officers were used to the darker and more extreme aspects of human behaviour: murders, drug violence, rapes.

This was something else.

The German news magazine Der Spiegel had devoted six pages and its cover to Litvinenko’s strange death. The date was 4 December 2006. Menzel picked up a copy and began reading. Halfway through he stopped. He reached for the phone. Spiegel reported that Kovtun had spent four days in Hamburg before meeting Litvinenko in London. Scotland Yard hadn’t been in touch but it was evident London’s problem was now Hamburg’s headache too. It was, seemingly, the biggest case since the discovery that some of the 9/11 terrorists led by Mohamed Atta had been living quietly in the city.

Menzel quickly established a few basic facts. Kovtun was registered in Hamburg, had an ex-wife in the city, and appeared to have lived in Germany for twelve years. The German authorities had no experience of polonium; nobody did. ‘We didn’t know what this substance was,’ he told me.

Menzel contacted two other federal agencies – the office of criminal investigation, known as the BKA, and the office of radiation protection. Soon, he had 600 officers on active duty. Journalists spotted lights burning in the Polizei-Stern over the weekend. Something was up.

Menzel’s team came up with a name for the unusual operation. They called it ‘Der Dritte Mann’ or ‘The Third Man’, after the black-and-white 1949 thriller set in divided post-war Vienna. ‘Der Dritte Mann is a film classic. We thought the title appropriate. We had three men who had gone to London and the atmosphere around it had something of the Cold War about it,’ Menzel said. He added: ‘It was very unusual. It had a political dimension like no other case I’ve been involved in.’

Within a short period, Hamburg police were able to reconstruct Kovtun’s movements in the city – from his ex-wife’s flat in Hamburg-Altona to the town hall where he filled in and signed his new foreigner registration documents. They found traces of polonium under his photo; indeed everywhere they looked. Officers lugged away evidence in boxes from Wall’s apartment in Erzbergerstrasse and from D3’s home. Menzel opened a criminal case. Kovtun was accused of unlawfully smuggling nuclear material into the Federal Republic of Germany.

Washington was paying attention. Duane Butcher, the US consul general in Hamburg, met Menzel on 14 December. In a confidential dispatch to the US State Department, later leaked, Butcher gave an account of Menzel’s findings. He noted: ‘Investigators hope to find out more about Kovtun as an individual – what he did for a living, what his personal background was – and whether he had worked at the Russian consulate in Hamburg in the past.’ Kovtun had met an Italian national in Hamburg – D3. Perhaps there was an Italian connection, Menzel told Butcher.

German and British investigators were agreed: the forensic evidence against Kovtun and Lugovoi was plentiful and damning. Butcher quoted Gerhard Schindler, deputy director general for counter-terrorism at the German interior ministry:

‘Kovtun left polonium traces on everything he touched – vehicles, objects, clothes, and furniture. German investigators concluded Kovtun did not have polonium traces on his skin or clothes; Schindler said that polonium was coming out of his body.’

As the investigation made progress, D3 found himself in a terrifying nightmare. After Kovtun flew to London he devoted no further thought to his friend’s wild story of traitors and poisons. Two days later, he called Kovtun to see how he was getting on. Kovtun didn’t pick up. A little later, and apparently back in Moscow, Kovtun called back, and said everything was fine.

Two weeks after that, D3 picked up a copy of either the Hamburger Morgenpost or Bild Zeitung – he can’t remember which. Splashed across it was the story of Litvinenko’s poisoning and death. Kovtun’s name was mentioned; he appeared to be the prime suspect. D3 read the story and, as he put it, felt the ground give way beneath his feet.

What he’d dismissed as another of Dmitry’s quixotic idiocies had materialised into a cold-blooded international killing. D3 was afraid and confused. He thought about going to the police. But what if this situation somehow rebounded upon him? He decided to do nothing. Perhaps detectives might solve the case on their own.

Then, Kovtun called from Moscow as D3 was out on his bike. The line was poor; they agreed Kovtun would ring again in the evening, which he did. Kovtun asked if D3 had read the newspapers. D3 asked him: ‘Was that you?’ Kovtun said the story was rubbish, adding that the English police were going to question him. ‘If that wasn’t you, you don’t need to worry,’ D3 replied.

Try as he might, D3 could not banish the poison conversation with Kovtun from his mind. In December, German police interviewed him for the first time. They searched his flat and took away his contaminated mattress. He gave them an account of his meeting with Kovtun. But he said nothing about Kovtun’s confession as they had walked together towards Steindamm.

As D3’s torment grew, Kovtun’s seemingly lessened. On 11 December, Kovtun phoned from Moscow. ‘He was quite jolly. He was in a good mood,’ D3 said. Kovtun said he was fine, apologised for causing inconvenience, insisted he was innocent, ‘marked’ by someone else and the victim of a media smear. D3: ‘I asked him what kind of arsehole he is to do this with Marina and the children? I was very angry but tried to remain calm.’ Upbeat, Kovtun was again talking of the Moscow flat he soon expected to receive.

They didn’t speak again.

D3 wasn’t afraid of Kovtun as such. But he understood that he was now a witness, an important one. And therefore – the logic had a dark certainty to it – a vulnerable one as well. It was a frightening position. Even if Dmitry were not capable of murder, perhaps others around him were? Twelve days passed. Unable to bear it any more, D3 told a lawyer what had happened. The lawyer contacted the police. ‘This awful feeling became so great that I had to get it off my chest. I had to say it, I could not go on,’ D3 said.

He told detectives the affair had left him uncertain and edgy. And added: ‘I curse him [Kovtun] every day, because of the conversation, because of the whole story, and because of other persons whom he has presumably also contaminated. And perhaps because of the mattress.’ His fear that something might happen to him or his family came and went, he said, adding: ‘I am frightened quite suddenly for no reason.’

Asked what might befall him, D3 gave a simple answer. ‘I may also be killed. I heard something,’ he said, adding that he felt guilty ‘because it then actually happened’. It never occurred to him to go to police immediately after the conversation, he explained, because he didn’t consider what Kovtun told him was actually possible.

German detectives were reluctant to believe D3’s account. They were sceptical for several reasons. First, they thought it unlikely that assassins sent by Moscow on a complex mission would be scrambling around at the last moment looking for a cook. Second, what kind of killer would suggest in the same breath that he and his ex-wife might strip off for a porno mag? It was … well, illogical. And improbable. And therefore dubious.

It wasn’t until 2010 that Scotland Yard – using cellular data and interviews with D3’s colleagues – established he was telling the truth.

In conversations with his friends and ex-in-laws in Germany, Kovtun stuck to the script: he was blameless. He called Eleanora Wall, his former mother-in-law, and said: ‘Please do not think that I did this.’ She believed him. ‘Dmitry is not a brutal person who kills people. No member of the KGB would have put poison in Dmitry’s hands,’ she told Hamburg detectives. ‘I do not believe when he visited us he knew he was giving off radioactivity.’

Only once did Kovtun let his guard slip – and then in ambiguous terms. Back in Moscow he was receiving regular infusions, he told Wall, as well as other medicines whose names he couldn’t reveal. Kovtun said he’d been exposed to some of the poison that did for Litvinenko. And told her: ‘These arseholes have probably poisoned us all.’ He didn’t explain who the arseholes were.

While Kovtun was calling Germany, the Russian authorities were busy covering up their role in the murder. Similar to the Metropolitan Police, Menzel tried to test the Aeroflot plane Kovtun had taken from Moscow to Hamburg. A team was got ready to ground it as soon as it arrived. Somehow, Russia’s spy agencies learned of the plan and at the last minute Aeroflot swapped planes. Kovtun’s plane never came back.

In Hamburg and London, the threads were coming together. The Met has been the focus of much public criticism but its investigation into Litvinenko’s murder was painstaking and exemplary. Around 100 detectives were involved, together with 100 uniformed officers.

Teams were sent out across the capital. Their job was to collect CCTV, identify potential witnesses and to find members of the public who may have been contaminated.

The public-health picture was a horrifying one. Forensic tests showed the murderers left radioactive traces at every location they visited: offices, restaurants, hotel rooms, toilets and aeroplanes. Scientists revisited each location with specialist detection equipment. They scanned every inch – leaving stickers with radiation readings in different locations.

This information was fed back to Scotland Yard’s computer-aided modelling bureau. It reproduced the findings in graphic form. Scientists also tested hair samples from Litvinenko. The results were revealing: they gave a window of dates for the two occasions on which he was poisoned. These coincided exactly with the dates of his meetings with Lugovoi and Kovtun.

The polonium appears on the hair as an area of darkness – first as a constellation of light dots and then as an intense, banded black region. The hair of a dead man.

I arrived in Moscow in January 2007, as the Guardian’s new Moscow bureau chief. My wife Phoebe and our two small children, Tilly and Ruskin, came too. We moved into a cramped temporary apartment in a tower block in the suburb of Voikovskaya. The kids’ new British international school was within walking distance; in the frozen courtyard youths were drinking from tins of beer. The cold felt sharp; it hit you in the face; you breathed it.

It was an inauspicious moment to be a British correspondent in Russia.

When Putin first became president in 2000, relations between Britain and Russia were positive. Putin’s first foreign trip was to London. Russia’s new leader – at this point an enigmatic figure, and the subject of the question ‘Who is Mr Putin?’ – called into Downing Street for talks. The prime minister Tony Blair hailed his guest as a fellow moderniser and defended him in the face of criticism over human-rights abuses and the new war in Chechnya. Putin even met the Queen at Windsor Castle.

The estrangement began in 2003, when a British judge granted Berezovsky political asylum. A court turned down Russia’s extradition request for Zakayev, whom it accused of terrorism. Putin took these decisions as a personal snub.

In the Russian system, judges typically do what the Kremlin expects of them. Putin interpreted the court’s rulings as a betrayal by Blair, who had failed to ensure the correct result. Russia lodged twenty-one applications for the extradition of Russian citizens from the UK. All were unsuccessful. Judges refused them on the understandable grounds that the individuals were unlikely to get a fair trial back in Russia and were, in many cases, being persecuted for their anti-government views.

Relations with the west in general were cooling, too. The Kremlin didn’t perceive the pro-western revolutions in Georgia, in 2003, and in Ukraine, in 2004, as popular movements for democratic reform. They were, it claimed to believe, the product of a US-engineered conspiracy. And a further sign of America’s insidious encroachment in Russia’s post-Soviet neighbourhood. US president George W. Bush – an early enthusiast for Putin – found that Russia’s president was a prickly and unpredictable adversary, opposed to Bush’s Iraq misadventure and much else.

From these alleged slights flowed a series of hostile actions by the Russian government. The British side did some daft things, too. In January 2006, Russian state TV broadcast footage showing an alleged British intelligence officer retrieving information from an artificial ‘rock’ concealed in a Moscow park. The 30-cm rock looked like a small, innocuous light brown boulder – the kind of boulder familiar to fans of The Flintstones. The FSB claimed UK diplomats used the rock to communicate with their Russian ‘agents’. (Jonathan Powell, Blair’s special adviser, later admitted the spy rock was genuine.)

Berezovsky remained a toxic figure for Putin’s administration. Just how toxic I found out for myself in April 2007. Two colleagues interviewed him in London. Berezovsky told them he was plotting nothing less than a revolution. He was, he said, bankrolling people close to the president who were conspiring to mount a palace coup. ‘We need to use force to change this regime,’ he said. Democratic methods were pointless – they wouldn’t work.

Berezovsky acknowledged that such statements were risky: ‘I don’t have any doubts that the Putin regime has become criminal, killing those they calculate as their personal enemy.’ Why? ‘Because they [the regime] identify themselves as Russia. Putin’s understanding is who is against him is against Russia.’

The oligarch’s latest claims were incendiary. He’d said similar things before but in less vehement tones. My bosses at the Guardian asked if I might get a reaction from the Kremlin. I reached Dmitry Peskov, Putin’s spin-doctor, and faxed over the key quotes to his office inside the president’s HQ. I had visited Peskov there before, soon after taking up my new Moscow job; he’d told me it was a sadness that the country’s opposition was weak.

The story appeared on the Guardian’s front page the following day, with a photo of Berezovsky and the headline: ‘I am plotting a new Russian revolution’. Peskov’s comments were included: ‘In accordance with our legislation [his remarks] are being treated as a crime.’ My by-line – Luke Harding in Moscow – appeared on the story, placed third, behind that of my two colleagues who’d done the work. At this point I’d never personally met Berezovsky or had any dealings with him.

A more self-assured regime would have dismissed Berezovsky’s claims as self-aggrandising baloney. They were ridiculous. Berezovsky didn’t have a secret army working inside Russian power. The FSB’s purpose, however, was to uncover plots against the state. Here – in lurid black and white – seemingly there was one. Someone inside the spy agency decided to hunt the conspirators. A good place to start, he thought, would be with the Guardian’s Moscow reporter.

I woke up the next morning to find myself inside a sort of sub-John le Carré spy novel. Over the next few weeks a succession of FSB agents followed me round the streets of Moscow. They were easy to spot: unpromising young men wearing cheap leather jackets and brown shoes. Once I met a friend in the deserted basement of a café. Two FSB operatives turned up ten minutes later and, ignoring the many empty tables, sat right next to us. They didn’t order anything; the spy agency doesn’t pay expenses for its officers on duty, I discovered. We laughed, and left.

It became obvious that someone was listening to my phone calls. The Guardian’s bureau was a ground-floor apartment in a block close to Moscow’s Belorusskaya train station. Two low-ceilinged apartments knocked into one. From the tiny kitchen you could see a small area of green where locals walked their dogs. I had a large desk with a landline. Whenever I called London and mentioned the word ‘Litvinenko’ or ‘Berezovsky’ the connection was cut. There was an ominous crackling. The same thing happened if I made jokes about Putin.

Other western correspondents experienced eaves-dropping too; the Brits and Americans were routinely monitored, it seemed. The KGB had perfected these techniques during the Cold War. Female agents listened to targets for hours on end in secret chambers dotted around Moscow. (This was tedious low-level work; it took hours to transcribe conversations.) A caller from the presidential administration, meanwhile, asked for my cellphone number. It looked as if someone had hacked my Gmail account too. Emails tagged with Berezovsky disappeared and then reappeared in my inbox.

None of this was perhaps surprising. Litvinenko’s murder had put a deep chill on UK–Russian relations; I was a British correspondent. The KGB taught its recruits that all western journalists were spies. The belief flowed from mirror thinking: in Soviet times, correspondents abroad, like the talented Yuri Shvets, used journalistic cover to conceal their real jobs as KGB operatives.

What was more unusual in my case were the break-ins by the FSB – a series of intrusions into the apartment where I lived with my family. These were sinister and unwelcome. They became a recurring feature of our Moscow life.

The first took place soon after the Berezovsky story was published. My wife was away. I had been at dinner with friends. I returned with Tilly and Ruskin to our apartment. We’d moved shortly before to a new tenth-floor flat in the suburb of Voikovskaya. From the living room there was a view of a park – birches and a municipal lake in one direction, where we swam in summer; a courtyard in the other.

That someone had broken in was obvious. My son’s single Ikea bed was next to a low window. We kept the window double locked. Now the window was unlocked. It had been left propped open – with a 15-metre drop to the yard below. We peered down. ‘Has there been a burglar?’ my son wondered. ‘I don’t know,’ I replied. It seemed unlikely you would survive a fall from such a height. The message appeared to be: take care, or your son might meet with an accident.

At 4 a.m. that night, I was woken by a loud beeping from next door. I turned on the light, and groped towards the sound. An alarm clock with a digital display was ringing in the living room. I hadn’t set the alarm. We’d inherited the clock from our landlord, Vadim, but never used it. It appeared my intruders had decided to play a sinister prank on us. Evidently, this wasn’t a conventional burglary. I checked the kitchen. I’d left several thousand dollars in a drawer to pay next month’s rent. The cash was still there.

Putin’s secret policemen were carrying out a different mission: to intimidate and scare us. Berezovsky, Litvinenko’s polonium murder, the FSB’s secret poison factory – all these were apparently taboo themes. I had crossed a line. There would be further break-ins, and further warnings.

Shortly before this covert harassment started, I attended Putin’s annual press conference. The venue was a giant two-tiered auditorium inside the Kremlin. This was a remarkable set-piece event – attended by 2,000 mostly Russian journalists and screened live on state television. They shouted softball questions. What did the president think about gardening? How should Russians bring up their kids?

Putin was also asked about Litvinenko. His dismissive response: that Litvinenko was a small-time agent who’d been fired from the FSB for beating up suspects and who ‘didn’t possess any secrets at all’.

In May 2007, the UK’s Crown Prosecution Service charged Lugovoi with Litvinenko’s murder. This, from Putin’s perspective, was another provocation. He refused Britain’s request to hand over Lugovoi. Putin said that Russia’s constitution forbids the extradition of its citizens. The request was a sign of Britain’s ‘arrogance’ and a ‘no brains’ colonial mentality, he added.

In the wake of the CPS’s charge, Lugovoi held a press conference. It took place in the Moscow office of the Russian news agency Interfax. This was the same room where in 1997 Litvinenko had accused the FSB of ordering him to snuff out Berezovsky. A photo of the famous event hung on a wall in the corridor. It was a hot day; I turned up in shorts. The room was full. Lugovoi walked in with Kovtun. Lugovoi was wearing a grey pinstriped suit and pink tie. Kovtun’s hair had grown back. Lugovoi began with a polite ‘Good afternoon, ladies and gentlemen.’

He said he’d called a press conference to defend himself from swirling accusations made by the ‘western mass media’. They had initiated ‘a real war against me and against Russia’, he said.

What followed was a lengthy denunciation – of Berezovsky, MI6 and the UK government, which had ‘hidden traces of the crime’ and ‘made me a scapegoat’. Lugovoi said that MI6 had tried to recruit him. He wasn’t a murderer, or as he put it: ‘Some Russian James Bond, infiltrating a nuclear centre and poisoning his mate in cold blood, contaminating himself, his wife and children along the way!’

Vesti-24, the state-owned TV news channel, broadcast this live. According to Lugovoi, British intelligence had murdered Litvinenko, one of its agents.

This was a serious allegation. I asked Lugovoi if he had any proof.

Lugovoi replied: ‘Yest!’ – There is proof!

So what was it?

Lugovoi didn’t offer details.

My question had annoyed him.

He said: ‘The British public must take a serious interest in what some Russian-born people are doing in the UK. They are engaged in recruiting Russian citizens, they sell British passports. The British nationality is for sale, esteemed BBC … sorry I don’t know what other English mass media companies are present here. Your nationality is sold like Chinese rags in a market, and you are doing nothing about it whilst thigh-slapping! I do apologise for the rough expression.’

Afterwards, the Kremlin announced that Lugovoi’s vague accusations – clearly based on talking points supplied to him by others – were worthy of ‘further investigation’.

Later that day, Britain’s ambassador to Moscow, Tony Brenton, sent off a confidential eGram – a diplomatic telegram – to the foreign office in London. Brenton summarised Lugovoi’s claims, noting that Kovtun ‘was present but said little’.

He concluded: ‘Lugovoi’s story sounds like nonsense to us, but is shrewdly judged for its plausibility to Russian ears – particularly in view of the “rock” incident last year. The fact that he was given nearly two hours on a government news channel to make his allegations strongly suggests official involvement in the stage management of his “revelations”.’

Britain’s security agencies compiled their own report on the murder, based on police evidence and secret sources. Its contents have not been divulged. The conclusion, it appears, is that this was a Russian state-sponsored assassination – not just an unfriendly act, but one involving dangerous nuclear material, which potentially endangered hundreds of lives.

In July 2007, the new UK foreign secretary, David Miliband, expelled four Russian diplomats from London. This was in protest at Moscow’s refusal to hand over Lugovoi. Miliband told parliament he believed the FSB was involved. He severed cooperation with the Russian spy agency and introduced a new visa policy for Kremlin politicians travelling to London. Up until this point MI6 had communicated with the SVR, its Russia’s foreign-intelligence counterpart. These channels were cut as well, even though the SVR was apparently not involved in Litvinenko’s poisoning, an FSB operation.

The Kremlin’s response was comparatively restrained. It expelled four diplomats in turn from the UK embassy in Moscow.

The mood among British diplomats based in Moscow was understandably embattled. They found themselves at the front end of the worst stand-off in relations since the Brezhnev era. Brenton held regular breakfast briefings for journalists. The ambassador’s residence was just off the Old Arbat – a nineteenth-century building in Bolshoi Nikolopeskovsky Lane that had once belonged to a merchant or senior official.

Brenton admitted that the Litvinenko case made better relations with Moscow impossible and said that there was no prospect of an early meeting between Putin and Gordon Brown, the UK’s new prime minister. ‘I don’t know what happens next. Lugovoi remains a wanted man,’ Brenton said. Lugovoi’s support came from the top and from ‘quite influential chunks of the Russian state’, he said, adding: ‘This guy is a suspected murderer. In normal places you don’t find a government giving support and encouragement to such a person.’

It was the use of a radioactive nucleotide that convinced the UK government this was a Kremlin plot, Brenton said. ‘Our private judgement is that you have to be a state or state organisation to get hold of polonium in the quantities it was used.’

The day after Litvinenko’s death, Lugovoi and Kovtun had visited the British embassy. They met Brenton’s deputy Sian MacLeod and his security officer David Chitty. The two Russians insisted they had nothing to do with the murder – and signed declarations to that effect.

Subsequently, the room was tested for contamination. Scientists picked up traces of polonium. The highest readings came from Kovtun’s chair – four to five becquerels per centimetre squared. They found it at the table in front of which Kovtun had been sitting, and in the storage hole where he’d left his mobile phone. ‘He sat in a chair. We had to burn the chair,’ Brenton said.

Actually this wasn’t quite true. Embassy staff locked the conference room used by Lugovoi and Kovtun, with the chairs still in it. Only a small number of diplomats knew about the radiation. Paul Knott, the embassy’s second secretary, told his colleagues the room wasn’t available because he’d ‘lost the key’. The atmosphere at the time was ‘sort of Le Carré’, he said, adding: ‘We had that Cold-War-is-here-again feeling. We knew things were worsening. But to do what they did in the heart of London seemed to us incredible.’

Brenton was an unusually frank diplomat. His reward was a campaign of Kremlin-sponsored harassment: the pro-Putin youth group Nashi picketed his public events, jumped in front of his car, and waved unflattering placards outside the embassy. The placards bore a photo of the ambassador with the word ‘Loser’ stamped in red ink across his forehead.

Days after my first break-in I had had my own meeting with MacLeod and an embassy security officer. I’d reported the intrusion to the Guardian and mentioned it to the embassy’s press attaché, who suggested I drop by. The venue for our chat was the embassy’s secure room from which mobile phones were banned. It looked rather like a music studio; a map of the Russian Federation hung on a wall. The room appeared to be the only part of the building which Putin’s security agents were unable to bug.

The conversation was helpful. And demystifying. It turned out the embassy knew all about FSB burglaries. They were Moscow’s worst-kept diplomatic secret, I learned. British and US diplomats and Russian nationals working for western missions found themselves on the receiving end of demonstrative break-ins. So, I later discovered, did Russian opposition activists. Recently, the break-ins had grown more frequent. ‘We don’t talk about it publicly. But no, you’re not going mad,’ the officer told me. ‘There’s no doubt this was the FSB. We have a thick file of similar cases. Generally we don’t make a fuss.’

The FSB’s tactics were weird, to say the least. They included defecating in loos, and not flushing afterwards; turning off fridges while the occupant was away on holiday; and introducing items of low value, like a cuddly toy, which hadn’t been there before. Sometimes a TV remote control would vanish, only to reappear weeks or months later. The same break-in team would install listening devices. Apparently, our flat was now bugged. ‘There’s not much you can do about them. Trying to identify or remove them will merely trigger the FSB’s return,’ the officer said.

On the surface, the FSB’s methods looked like bad-taste practical jokes. Actually, the KGB knew that such tactics – repeated over time – could have a destructive effect. The KGB developed and codified these techniques in the 1960s and 1970s. They had a name: operational psychology.

The Stasi, East Germany’s secret police, and the KGB’s sister organisation, employed the same tactics against dissidents, church leaders and others. One former Stasi officer told me proudly: ‘We always did it better than the Russians.’ Such methods were wonderfully deniable. It was easy to deride anyone who complained of sprite-like intrusions by unknown third parties as paranoid and mad.

I discovered that Stasi officers had written entire theses about what they called Zersetzung. The word in German means corrosion or decay. The goal of this harassment – in which the state’s hand remained hidden – was to ‘corrode’ a target so he or she ceased all hostile anti-state activity. With me, that appeared to be writing articles on themes the FSB deemed unacceptable. In the GDR, Zersetzung became a pseudo-scientific discipline. Putin had certainly come across Zersetzung when he served as a junior KGB spy in Dresden.

The embassy officer told me there was no evidence the agency hurt children, despite the ominous window left open next to my son’s bed. This was somewhat consoling.

That summer I received a letter from the FSB. It said that the agency had opened a criminal inquiry into Berezovsky’s Guardian interview. It added that Berezovsky had taken part in activities against state power, an offence under Russia’s penal code, article 278. An FSB agent called our Moscow office. He informed me I was being summoned as a ‘witness’ in connection with the case. I was to report to Lefortovo Prison. Oh, and I’d need a lawyer.

Three weeks later, I turned up outside Lefortovo jail. The letter had indicated the address – Energeticheskaya St 3a – useful since Lefortovo didn’t appear on maps. The building was as forbidding as I’d imagined, set among anonymous grey apartment blocks. There was a single tree in the courtyard. I entered through a heavy metal door with my lawyer, Gari Mirzoyan. Inside there was a large waiting room. It was devoid of tables and chairs. The agent on duty sat behind a silvered one-way window. He could see us; we couldn’t see him.

A hairy hand shot out and took my passport. Since there was nowhere to sit, we stood. After five minutes we were told to proceed to room 306, where Major Kuzmin was waiting for us. We walked down a corridor. The carpet was a worn red-green. I noticed an old-fashioned lift, with a heavy metal grille. It sank to the prison’s lower depths where Litvinenko had been kept. Above us were old-style security cameras. The atmosphere was one of shabby menace and institutional gloom. Seemingly little had changed since KGB times.

Major Kuzmin was younger than I expected: late twenties perhaps, with blond hair, neatly cut, and wearing a dark olive-green uniform. Lying on his desk was a colour photocopy of the Guardian’s front-page Berezovsky scoop. I had explained that my role in the affair was a small one. Nonetheless, Kuzmin wanted to know under what circumstances the interview had taken place. Who was present? Was there a recording? Kuzmin typed my replies – there wasn’t much to say – two-fingered onto a computer.

It occurred to me that Kuzmin probably wasn’t the officer’s real name. Was he the guy who had been organising my apartment break-ins? There was nothing in the room that gave clues to his personality – no photos, one small spider plant. On the table in front of me was a bottle of fizzy water and a glass. Drinking didn’t seem like a good idea. The glass was engraved with four sets of initials in Cyrillic letters: Cheka, OGPU, KGB and FSB. These were the names of the Kremlin successive counter-revolutionary agencies, beginning with Dzerzhinsky’s Cheka.

After fifty-five minutes, the interview was over. Kuzmin gave me a witness statement to sign. We shook hands. He offered me a gift: a copy of the ‘Investigations department, Lefortovo Prison’ 2007 FSB calendar. It featured the FSB’s sword and shield logo, in dark red, against a purple background. Mirzoyan and I walked out into the corridor. It was empty. There was no noise or office chatter – merely a smooth and unnerving silence.

Despite the apparent end of the Cold War, the FSB clearly saw itself operating in the same tradition of Bolshevik conspiracy as its predecessors. The KGB’s and FSB’s goals were the same: to protect the state against all enemies. The agency’s neuralgic reaction to a single newspaper article suggested the Kremlin continued to view Berezovsky as its enemy in chief, a sort of modern Trotsky. Apparently I’d been marked down as Trotsky’s mini-helper and accomplice.

The FSB’s Lefortovo summons had the opposite reaction to what the agency may have intended. The Litvinenko case was inherently fascinating – and I was being told, through unsubtle KGB-style break-ins, not to investigate. The Kremlin’s extreme sensitivity to the topic suggested there was a lot to uncover. With digging and a little tenacity, perhaps it might be possible to find some answers.

In the summer of 2007, I met Dmitry Peskov, Putin’s urbane English-speaking press spokesman. It was a moment when the Kremlin still cared about Russia’s image abroad, one the Litvinenko affair had dented. A group of western correspondents had been summoned to one of Moscow’s fancier Italian restaurants. Peskov explained the affair from the Russian government’s perspective.

In his version of events, the Kremlin was a blameless victim: a reasonable and forbearing partner, surrounded by hostile and irrational actors. Miliband’s decision to expel four Russian diplomats was ‘totally unexpected’, Peskov said, and a throwback to the bad old days of Cold War confrontation. ‘We consider it unfortunate,’ he added smoothly, his tone – this was classic Peskov – one of faux innocent regret.

Peskov stated that Moscow ‘strongly rejected’ any suggestion of Russian state involvement. Where was the proof? Litvinenko’s death was a ‘terrible crime’ and not a political murder, he said. He reeled off Moscow’s many grievances against London – unsuccessful extradition requests, ‘Mr Berezovsky, Mr Zakayev…’ One quip had annoyed him. Peskov recalled how he flew first-class with British Airways from New York to London. The stewardess had served him a cup of tea with the words: ‘No polonium this time, Mr Peskov.’

According to Peskov, London was succumbing to the kind of virulent ‘Russophobia’ more usually associated with Eastern European countries like Poland. ‘You want me to encourage my citizens to go to London?’ he asked, adding: ‘It takes two to tango.’ He was adamant the Kremlin was reacting to the aggressive behaviour of others. ‘We weren’t the initiators of this crisis,’ he said. ‘This mirror response [the expulsion of UK diplomats] was actually something we regret, and something we were forced into.’

Peskov’s performance reminded me of the writer and critic Clive James’s observation in his book Cultural Amnesia: truly unprincipled states never blush.

Meanwhile, the FSB sent me a further letter. Its investigation was going well; officers had concluded that I didn’t meet Berezovsky. I was therefore ‘not of interest’ to the agency, it wrote. In August we flew back to the UK for our annual summer holiday and a week on a Cornish beach. Later that month I returned to Moscow without my family, who were staying on.

The post in Moscow was unreliable; sometimes packages arrived, sometimes not. I had hand-carried a video taped by a friend, the poet Heathcote Williams. He had recorded two documentaries he thought might be of interest. One was a BBC Panorama investigation into Litvinenko’s death, How to Poison a Spy, presented by the journalist John Sweeney. The other was My Friend Sasha – a Very Russian Murder by Andrei Nekrasov, the filmmaker who had shot the deathbed footage of Litvinenko.

I dumped the tape under the TV, and forgot about it. Williams had Sellotaped programme notes to the side of the cassette, including the photo of Litvinenko in intensive care. One Sunday evening I slotted the video in to watch. The recording began normally – a slice of BBC Newsnight hosted by Jeremy Paxman. After this, something very strange. The Litvinenko documentaries had been erased. Instead of pictures, there were scratchy black-and-white lines; the sound, just audible, was a high-speed squeak.

It was hard to be sure, but it appeared the FSB had broken in again, taken umbrage at the tape’s contents, and deleted them. I emailed Williams. He’d checked the tape before he sent it; it played fine. The Panorama documentary, I found out later, featured interviews with all the major players. Peskov – who else? – denied Kremlin involvement.

There was also a clip from an interview with Litvinenko. In it, he remarked: ‘There were two ideologies in the Soviet Union, communist and criminal. In 1991, the communist ideology ceased to exist and only the criminal remained. The KGB was renamed, it became the FSB, but nothing really changed. Everything stayed the way it was before. The only difference was that a KGB officer killed for his ideology while an FSB officer kills for money.’

Lugovoi had friends in high places; that was obvious. They were keeping a close eye on his case. I caught up with the man himself four months later. He was on the campaign trail, embarking on an unlikely career as a deputy in Russia’s parliament. Lugovoi was number two on the federal list of the Liberal Democratic Party of Russia (LDPR), an outfit set up by the KGB and led by the flamboyant Zhirinovsky. In his new role as a would-be politician, Lugovoi zigzagged across the country, traveling to the Far East, the Urals and European Russia.

It seemed that Lugovoi was going to make the best of his notoriety. His campaign, such as it was, had an anti-British flavour.

I went with Lugovoi to Manturovo, a village 60 miles (100 km) outside the western city of Kursk. It was always good to get out of Moscow; here were crumbling dachas, snow-covered fields and poplar trees. Lugovoi toured a farm, peered into its cowshed and visited an orphanage. That evening he talked to locals in a pink-walled hall decorated with an icon and a bust of Lenin. His audience listened politely.

Lugovoi, it struck me, wasn’t a natural politician. With his modish suit, purple tie with swirls and Italian shoes, he cut an incongruous figure. Since elections in Russia were fake political exercises – vote rigging on behalf of the ruling United Russia party was rampant – this didn’t matter. At a press conference in his hotel, the Nightingale, Lugovoi blamed Britain for Russia’s woes. The British had invaded Crimea, forged the Zinoviev letter in 1924 and carried on behaving like ‘Anglo-Saxon imperialists’.

I scribbled his remarks in my notepad. ‘If you look at Russian–British relations, the Cold War never started and never ended,’ he declared.

Locals seemed bemused by his performance. Did it matter that Lugovoi was accused of murder? ‘It’s difficult to say,’ Viktor Shumakov, a veteran of the Soviet war in Afghanistan, told me. ‘In Russia many strange things happen all the time.’

A year after Litvinenko’s death, Lugovoi was elected as a deputy to Russia’s Duma. His meteoric rise, most observers in Moscow felt, could have happened only with the Kremlin’s endorsement. Lugovoi, meanwhile, gave numerous audiences to the domestic and foreign press. They took place in Moscow, on the remote and beautiful Kamchatka peninsula, and while he sat on the back of a horse.

My own on-off investigation into Litvinenko’s murder had not met with a breakthrough. But there were clues. I went to see Olga Kryshtanovskaya, an expert on elite politics, and a researcher in sociology at Russia’s academy of sciences. Kryshtanovskaya was an interesting figure, who would go on to became a United Russia MP. She had described how under Putin former KGB officers rose to senior positions – by 2007, 42 per cent of those in top Kremlin jobs had a military or intelligence background. She had good contacts inside Russian intelligence.

I asked her about Litvinenko. She said that FSB officers had privately admitted that his murder must have been one of their operations. They had no regrets about the target – Litvinenko was a traitor and merited the punishment – but expressed surprise at the shoddy way in which his execution was carried out. These things were done much more tidily by the KGB, in particular when Yuri Andropov – the only KGB officer to lead the Soviet Union – was communist party general secretary.

‘My FSB friends told me that this [Litvinenko’s bungled poisoning] would never have happened under Andropov,’ Kryshtanovskaya told me. ‘They told me the KGB was much more efficient at murdering back then.’

Lugovoi and Kovtun may have been third-rate killers, but they continued to enjoy support from where it mattered. In April 2008, I interviewed Lugovoi for the first time. The location was his first-floor office in Moscow’s Radisson Hotel in Kievskaya, the same place where the detectives from Scotland Yard had stayed.

Despite his contempt for the British ‘establishment’, Lugovoi turned out to be an Anglophile. He was a fan of English literature; the works of Arthur Conan Doyle sat in a glass-fronted cabinet case. ‘I’ve read all Conan Doyle. I’m very fond of The Lost World,’ he explained. His son went to the same British school in Moscow as my son, though at a different campus. His daughter spent a year on an English course in Cambridge.

Lugovoi’s assistant, Sophia, brought us tea. On the wall was a photo of Putin shaking hands with Berezovsky; another jokey montage showed the president chopping the head off the exiled oligarch Mikhail Khodorkovsky. There were framed snaps from Lugovoi’s days in the Federal Protection Service, when he accompanied Kremlin politicians including Boris Yeltsin and prime minister Yegor Gaidar. I spotted two photos of his trips with Gaidar to Washington.

I asked Lugovoi why he had joined the KGB’s ninth directorate, responsible for government security. ‘They invited me. Any normal Soviet officer would take it as an honour to be in the KGB. It means that you are the best.’ Lugovoi denied that he was ever a spy and said his job in the early 1990s, as head of a Kremlin platoon, was rather boring. Instead of intelligence work he trained new recruits to perform ceremonial drills in Red Square.

What happened in London? Lugovoi’s answer: nothing much. He claimed Litvinenko insisted on a meeting, picked the Millennium Hotel as venue, and called him ‘at least five times’. This was, as phone logs later demonstrated, untrue: it was Lugovoi who called Litvinenko. As for the tea: ‘I’ve always said I can’t remember whether we ordered tea at all. I remember that I drank some whisky or gin. Then Litvinenko arrived. He said next to nothing. He was very excited.’

Not all of what Lugovoi said was deceitful. He recounted how Litvinenko rang him at 8.30 a.m. on 2 November and explained he was feeling ill and couldn’t make their meeting later that morning. Lugovoi phoned Litvinenko in hospital on 7 November (‘We had an excellent conversation’) and on 13 November – the last call before his death. Lugovoi said Litvinenko had told him he worked for British intelligence: ‘He was definitely an agent of the English security services.’ Lugovoi took a dim view of MI6, which recruited its agents ‘in the pub’.

It was strange. Lugovoi had a certain charm. In person he was disarming. His tale of virtuous innocence and wrongful insinuation even seemed plausible, until you remembered the chilling facts. He smiled, joked, made rueful expressions with his face, and tossed the occasional word of English into his Russian (‘absolutely’). He was wearing the same kind of clothes – a pink shirt, fashionable cuffs, grey business suit – that had prompted hotel staff in London to snigger.

By this point, Lugovoi had given dozens of interviews to journalists. In each, he stuck to the same blameless formula: he wasn’t a murderer but the victim of conspiracy. At key points, his recall of events was fuzzy. Why couldn’t he remember what drinks he ordered at the Millennium Hotel? It wasn’t an encounter you would forget. He was lying, there was no doubt. Underneath his smooth persona was something cold, cruel and terrifying.

Before my interview with Lugovoi, I bumped into Kovtun outside the office. When I emerged he was waiting for me. He had the air of someone with not much to do. Though he didn’t say so, he seemed jealous of Lugovoi’s fame and obvious material success. In the wake of the CPS’s murder charge, Lugovoi became, for many Russians, a national hero. Kovtun – not charged until 2011 – was a footnote.

We chatted for ten minutes. Kovtun said his situation frustrated him. His attempts to clarify whether he was under suspicion had been unsuccessful. He wanted to go back to Germany but not if that meant arrest and jail. ‘There are no guarantees. I don’t want to risk it,’ he told me. Kovtun said that he was still on good terms with his ex-wife Marina, who had visited him in Russia over New Year. She’d remarried, had kids, started a new life.

Kovtun said he ended up in the Pine Bar because of a series of coincidences – in Germany his passport renewal went quicker than he expected; he and Andrei sat in the bar because Lugovoi’s family hadn’t returned from Madame Tussauds. But what about the polonium? The trail went to his hotel bedroom, didn’t it? ‘By the time the polonium was found, twenty days had passed. There was plenty of time for the British intelligence services to organise lots of things,’ he replied.

Kovtun wrote down his mobile number for me. He was stuck in Russia, but felt things could be worse. ‘We go on holiday in Siberia and Altai,’ he said. ‘It’s a big country.’

Not long after our conversation, Kovtun broke off all contact with Lugovoi. After 2009 they maintained no relations whatsoever. The two murderers, for whatever reasons, had fallen out.

One of Russia’s most popular social networking platforms is LiveJournal.com. Alex Goldfarb ran a page on the site devoted to the Litvinenko case. One day, Goldfarb received an intriguing email. Its sender, ‘thepotemkin’, said he had information that might be of interest. It concerned polonium.

Goldfarb suggested that he and the source – his name was Alexei Potemkin – communicate via Skype. Potemkin explained his background. He was, he said, an FSB agent working undercover in Austria. He claimed to have met Litvinenko in the mid-1990s. And been part of the transportation chain that smuggled the polonium from Russia to London.

Goldfarb was wary. Was this an FSB set-up? He met Potemkin in Austria four times. It turned out Potemkin was disillusioned with his job – spying on Austria’s Chechen diaspora – and wanted out. Potemkin said that in 2006 an FSB courier delivered a sealed container with radioactive markings. His job was to deposit it with left luggage at Innsbruck Station. The package was the size of a photo. In it was a sealed vial. The vial had a coded lock.

According to Potemkin, the FSB began to carry out espionage missions abroad from 2000. The SVR, Moscow’s foreign-intelligence agency, resented this. Potemkin said his ultimate boss was Mikhail Nechaev. Nechaev, a three-star general, was the head of the FSB’s counter-intelligence operations department and a very powerful figure.

This was fascinating – but, as Goldfarb recognised, meant little without documents. Potemkin said that in 2003 he’d attended a meeting with Nechaev in Moscow in which polonium was discussed. It had a codename: ‘chemistry’. A representative from the FSB’s research institute in Moscow described it as ‘a perfect poison’. It couldn’t be detected by standard police or hospital equipment, the officer said, and was ‘harmless unless ingested’.

Potemkin gave Goldfarb internal FSB waybills. They appeared to confirm what Professor Dombey claimed – that the polonium came from the Russian nuclear production facility at Sarov. From there, it was sent to another nuclear complex at Balakovo, 250 miles (400 km) away. A driver from the FSB’s garage in Yaroslavl collected the polonium, and delivered it to the FSB’s research institute in Moscow. The shipment took place six to eight weeks before Litvinenko was poisoned.

Goldfarb believes Potemkin’s story is genuine. ‘My personal sense is that there is no sense in him inventing all this,’ he said. ‘It would be too dangerous.’ Potemkin agreed to seek asylum in the UK, holing up for a week at a pension in Vienna, but then changed his mind. He went to ground in a secure place somewhere in Europe. The last contact was in late 2010.

Others are not so sure. Andrei Soldatov, a Moscow-based journalist and expert on Russia’s spy agencies, says that some details on the documents are wrong. For example, one is stamped ‘FSB counter-intelligence service’. At the time, back in 2003, it was still an FSB department, not becoming a service until 2005.

And what of General Nechaev, the man who may have masterminded the Litvinenko operation? In December 2007, he died. He was fifty-six. Potemkin told Goldfarb he didn’t believe Nechaev’s death in Moscow was due to natural causes. Rather, it was punishment for the fiasco in London. Polonium was never meant to be discovered. Nechaev’s team was disbanded, Potemkin said.

The FSB posted Nechaev’s obituary on its website. The citation was brief. ‘Mikhail achieved significant results in the confrontation with foreign intelligence agencies,’ it wrote.

Back in Moscow, the intrusions at our apartment continued; the FSB would typically break in after I wrote something which displeased them. The UK Foreign Office raised my case privately with their Russian counterparts. The harassment would stop, only to resume a few months later. By 2010, I wondered how my Moscow assignment might end. Perhaps I would leave normally, when it was time to move on. Perhaps not.

My newspaper was on a roll: publishing a series of articles in collaboration with WikiLeaks, based on leaked US military logs from the wars in Afghanistan and Iraq. That autumn I flew back to London to take part in a third investigation. There was another leak. It was sensational – more than a quarter of a million secret and classified dispatches sent from the US’s embassies and consulates around the world, back to the US state department in Washington.

My task was to examine the cables on Russia and the former Soviet Union. There were 3,000 of them. I and other correspondents worked in an airless room – the air conditioning was broken – on the fourth floor of the Guardian’s Kings Cross office. A search engine allowed you to enter a term that would spill out a set of results. You could also specify which US mission was of interest – Moscow, Paris, Berlin etc. I took a breath. I entered a search term – ‘Litvinenko’.

At a glance, the results were disappointing. The secret cables didn’t reveal who ordered Litvinenko’s murder; apparently Washington didn’t know. Or, if it did, this wasn’t a subject for diplomatic traffic. I looked again. Bingo! The most interesting material came not from the US embassy in Moscow but from elsewhere. I found the secret Madrid cable citing Litvinenko’s work for Spanish intelligence and his thesis that Russia was a ‘virtual mafia state’.

Another intriguing telegram came from the US mission in Paris. It suggested the White House believed Putin knew about, and probably approved, Litvinenko’s murder. Sent on 12 December 2006, it noted a meeting between the US assistant secretary of state, Daniel Fried and Maurice Gourdault-Montagne, a French presidential adviser to Jacques Chirac. The French blamed Litvinenko’s poisoning on ‘rogue officers’. They doubted the Kremlin was involved.

Fried disagreed: ‘Fried, noting Putin’s attention to detail, questioned whether rogue security elements could operate in the UK, no less, without Putin’s knowledge. Describing the current atmosphere as strange, he described the Russians as increasingly self-confident to the point of arrogance.’

There were other striking cables. I discovered that I wasn’t the only one suffering from covert FSB tricks. In 2009, the US ambassador John Beyrle, complained that ‘harassing activity against embassy personnel has spiked in the last several months to a level not seen in many years’. It included libellous attacks against US staff in the Russian media, and claims – made to family members – that their loved ones had met accidental deaths. Beyrle also said: ‘Home intrusions have become far more commonplace and bold.’

The Russia WikiLeaks material was terrific. It was known that the country suffered from corruption and misrule. The cables went further. They suggested the US shared Litvinenko’s gloomy conclusion that Russia had morphed into a full-blown kleptocracy run along mafia lines. In December, the Guardian ran a front-page story with the headline: ‘Inside Putin’s “mafia state”’. An article citing the Fried cable together with a photo of Litvinenko ran on page two. I was the author; they appeared with my by-line.

Before I flew to London the press and information department of Russia’s foreign ministry summoned me to a meeting. I’d been informed my press accreditation and visa would not be renewed. The British embassy succeeded in postponing this decision – I had to leave by December 2010 – for six months. This would give us enough time to pack up our home, find new schools for the children, and move back to the UK.

In the meantime, the WikiLeaks articles had enraged someone in the FSB, or the presidential administration, or both. In February 2011, I flew back from London to Moscow, and found myself dumped out of Russia. Officials from the Federal Migration Service cancelled my Russian visa, locked me briefly in a cell, and then escorted me back to the plane I’d just arrived on. My four years as Moscow bureau chief ended in expulsion.