LONDON — Intimidation, breaking and entering, double-crossing, and a suspected poisoning—the extraordinary inside story of Moscow’s battle to block an investigation into the murder of a Russian dissident can be told for the first time. And it’s an object lesson about “cooperation” with Russia’s Vladimir Putin.

The Scotland Yard detectives who followed a trail of alpha radiation from London’s ritzy Mayfair to the heart of Moscow have broken their silence in a documentary that will be broadcast in Britain next week.

In the weeks after Alexander Litvinenko was given a deadly dose of polonium-210 from a teapot in a Central London hotel, Russian authorities assured the British government that they would cooperate with the investigation and allow police officers to interview the two prime suspects in Moscow.

As soon as the detectives landed in Russia in December 2006, it became clear that the authorities were not there to help. There had been no public announcement of the mission to secure evidence in Moscow but a phalanx of photographers and videocameras greeted their arrival at the airport.

The message to the officers was clear: We are watching you.

“It was supposed to be a top-secret trip, but their cover was immediately blown,” the documentary’s BAFTA-winning producer Richard Kerbaj told The Daily Beast.

MI6 had warned the detectives about using cellphones, bugging, and honey traps before they left. “It was very much intimidation—you have your overt covert and your covert covert intelligence. It was just so obvious,” said Kerbaj.

“They were playing by the British rulebook and the Russians were there to undermine the investigation from the very beginning.”

The first man suspected of involvement in the assassination of Litvinenko was former KGB agent Dmitri Kovtun. After a series of delaying tactics, Scotland Yard detectives were finally given his whereabouts—they jumped straight into their vehicle and asked their Russian driver to race to the hospital where they were told Kovtun was suffering from polonium poisoning.

Instead of driving directly to the hospital, the driver took repeated wrong turns as though he was deliberately slowing their journey. After a few U-turns, they arrived at the hospital to find a man completely disguised beneath medical equipment and bandages.

“The only thing that you could see was the eyes. It could have been anyone sat in the bed. We will never know who it was,” former Detective Inspector Brian Tarpey told the Channel 4 documentary Hunting the KGB Killers.

After just a few minutes of questions—which the Russian authorities said they would record on behalf of the Scotland Yard inspectors—they were told their time was up.

As they waited for their next major interview, events continued to infuriate the officers. They were frequently followed; their questions went unanswered; and small pieces of paper placed in drawers and bags as traps to show signs of tampering were disturbed while they were out of their hotel.

The former head of Scotland Yard’s Counter Terrorism Command, Peter Clarke, said: “To put it simply, they were messed about. The Russians kept saying ‘We’re cooperating,’ but it was unlike any cooperation that I’ve ever seen.”

During one meeting at the prosecutor general’s office, Tarpey was offered a drink. “I had a cup of tea and we left. I started to feel a little uncomfortable, and not wanting to put too fine a point on it I had the shits. I have no doubt in my mind that we were probably poisoned with something like gastroenteritis. I think that there was a deliberate ploy to weaken us physically,” he said.

On Monday, the second suspect, Andrei Lugovoy, was asked about the poison claim by British investigators. “They were here in 2006, we met,” he told RBC daily. “As for their tea poison allegations, I can only say that either they have gone mad or they’ve read too much of Conan Doyle.”

During that meeting with Lugovoy, the detectives had a bit of trouble as the authorities said the suspect didn’t speak English and everything had to be done through translators. Still, they’d be able to go back over the tapes when they got home.

“I thought that, well this has been recorded so we will get what it is that’s been said and we can compare that to the notes that have been taken. At the end of the interview, Lugovoy kind of smirked and said, ‘Good luck with your investigation’ in English,” Tarpey said.

At the end of the trip the British detectives collected the packets of evidence, which the Russian authorities had insisted they keep, and boarded the plane back to London. When officers went through the files—the Lugovoy tape was gone.

“What was probably the most important output from that whole deployment, it never made it on the plane,” said former Detective Chief Superintendent Clive Timmons, who ran the operation. “Was it an accident? Nah. It didn’t tell me that Tarps or anyone else had been unprofessional. It told me we’d been done.”

It was looking as though events in Moscow would prove Timmons’ cynical old Scotland Yard colleagues right. Some of the more experienced detectives recalled the assassination of Georgi Markov, a Bulgarian dissident in London, whose 1978 murder with a poison-tipped umbrella was never solved.

“Some of the senior rank were saying, ‘Yeah you are never going to solve it. You are never going to get near solving it,” Timmons said with a determined look on his face. That only doubled his resolve.

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The first breakthrough came while Litvinenko, who was known as Sasha to his friends, was still alive. “Post mortem is one of the most valuable tools in informing murder enquiries and Sasha was obviously living—so I wanted to do the equivalent of a living post mortem,” Timmons said.

The doctors had ruled out thallium, a heavy metal suspected by Litvinenko, and they had ruled out all nuclear materials because polonium gave off different kind of radiation and had not been detected. They told detectives that they might never know what had effectively liquefied the insides of an otherwise healthy man.

Timmons overruled the medical team and sent a urine sample to Britain’s Atomic Weapons Establishment. They said they had found a tiny trace of polonium. “I was thinking we have all grown up watching James Bond, we all know plutonium we all know uranium, so I say ‘Polonium? Don’t you mean plutonium?’ And so, this fella—very tolerantly—says, ‘No, Clive, I mean, polonium-210.’ ‘What’s polonium-210?’ ‘It’s the most toxic substance known to man.’”

The method of murder had been ascertained, but not the weapon itself. Again, it took Timmons’s instincts to ignore the expert advice he was being given. He ordered a laborious full test of all of the crockery at the Millennium Hotel where Litvinenko had met Lugovoy and Kovtun, even though he was told all traces would have been washed away after weeks of going though their dishwashers.

The results came back and, boom, there was the “smoking teapot.”

Vladimir Putin, who was accused of ordering the hit, says Kovtun and Lugovoy, who deny the charges, will not be extradited for trial in Britain.

They will never be jailed for the crime which they were formally accused of perpetrating during the Litvinenko inquiry in London last year, but the detectives and Litvinenko’s wife, Marina, are satisfied that the murder has been solved.

“Marina now knows her husband’s story has been told and if it is disputed, well, then the people it applies to, they can happily bowl up here and have their day in court to explain their story,” Timmons said.

Hunting the KGB Killers will be broadcast on Britain’s Channel 4 on Monday, April 17.