In a nearly windowless courtroom in the east wing of London's Royal Courts of Justice, an inquiry is underway that bears all the trappings of a James Bond thriller.
Headed by a former high court judge, the investigation is seeking to establish whether former Russian spy-turned-MI6 informer Alexander Litvinenko was fatally poisoned in 2006 by radioactive polonium-210 slipped into his tea by two former KGB agents at one of London's most prestigious hotels.
Prosecutors are convinced that the men Litvinenko met with were responsible for his death and that it was a calculated, state-sponsored plot orchestrated by Russia's spy agencies, authorized at the top level of government. The highest level, in fact.
The pair, witnesses say, left a trail of the deadly, difficult-to-identify isotope in hotel rooms, restaurants and airplanes. Ultimately, they believe, that trail leads all the way to Russian President Vladimir Putin, who some think personally ordered the killing of Litvinenko, an outspoken critic of the Kremlin.
As fantastic as the evidence sometimes sounds, with mentions of men in wigs wearing sunglasses and homes being firebombed, the inquiry is not a movie plot but a window on modern-day espionage.
It portrays Putin as ruling through corruption and an iron fist, as well as a British government struggling to rein in an autocrat who refuses to be accountable, and it cuts to the core of the fragility and complexity of British-Russian relations in the post-Cold War era.
"It was an act of nuclear terrorism on the streets of a major city, which put the lives of numerous other members of the public at risk," Ben Emmerson, the lawyer representing the Litvinenko family, said in his opening statements. "The trail of polonium traces leads not just from London to Moscow but directly to the door of Vladimir Putin."
The gripping public inquiry, which began two weeks ago, is expected to last more than two months and hear from more than 70 witnesses. Chairman Robert Owen will issue a report, but cannot make findings of civil or criminal liability.
Among those who have testified are Litvinenko's wife, Marina, and their son, Anatoly, who recalled his father speaking passionately about the "honesty and transparency" of the British judicial system, compared with that of Russia.
Russia has refused to extradite the two men the British government believes killed Litvinenko, one of whom is now a deputy in the Duma. The men have denied being involved in Litvinenko's death, but have declined to provide testimony via video link.
Requests by Marina Litvinenko for a public inquiry were at first denied, partly, Home Secretary Theresa May acknowledged, for fear of offending Russia.
Marina Litvinenko appealed and her wish was finally granted, coincidentally or not, days after Malaysia Airlines Flight 17 was shot down over eastern Ukraine by pro-Russia rebels last year.
"This is as good as you get when you can't get an extradition," Marina Litvinenko's lawyer Elena Tsirlina said.
The events leading to what prosecutors believe was Litvinenko's brazen assassination stem from his career as a spy for the FSB, the successor to the KGB, where he specialized in organized crime.
In 1998, he publicly accused his bosses of seeking to kill oligarch Boris Berezovsky, and was swiftly blacklisted by Putin, then head of the FSB.
Litvinenko's family was threatened and he was prosecuted in Russia on "trumped-up charges" twice, though acquitted both times, Emmerson said.
When he heard he was to face a third set of charges, it was time to leave.
A complex operation to get the Litvinenkos safely out of Russia was set in motion with the aid of a network of well-connected Russian defectors. The family fled to neighboring Georgia, then Turkey and on to London, where, after arriving in 2000, Litvinenko claimed political asylum.
Berezovsky, who by that time had also fled to Britain, covered their expenses, amounting to $130,000 and a $6,000 monthly stipend, according to testimony by Alexander Goldfarb, a close friend who was with the family at the time.
The Litvinenkos moved into a house in a leafy middle-class area in the north of London, across the road from former Chechen separatist leader Akhmed Zakayev, whom Berezovsky was also helping financially.
But Litvinenko was unable to leave his past behind. The inquiry has repeatedly portrayed him as an obsessive man ferociously committed to exposing corruption and criminality within the Kremlin.
"He wouldn't stop," said Goldfarb, whose testimony was considered so sensitive that reporters had to watch via a video stream with a five-minute delay.
Litvinenko wrote two books in Britain, claiming among other things that deadly 1999 Russian apartment bombings that took nearly 300 lives were carried out by FSB officers to justify the second Chechen war and influence the political landscape, which ultimately brought Putin to power.
Litvinenko earned $2,000 a month from MI6, the British intelligence agency, from 2003 on as an organized crime specialist.
After the publication of his books, one former FSB colleague warned him to get his will ready. "You have been sentenced for out-of-court elimination," the email read.
His widow described someone "from the Russian Embassy" ringing their doorbell unannounced, and testified that their home and that of neighbor Zakayev were firebombed.
A final nail in Litvinenko's lead-lined coffin came when Russian journalist Anna Politkovskaya, a critic of Putin, was killed only weeks before his own fatal poisoning. Incensed, Litvinenko attended a meeting at London's Frontline Club where her life and death were discussed.
"Mr. Putin murdered her," he told the audience.
On Nov. 1, Litvinenko met with former KGB agents Andrei Lugovoy and Dmitry Kovtun, he said in a statement to police on his deathbed. He said the plan was to meet to discuss a business deal.
Lugovoy arrived first, and was drinking green tea from a silver teapot.
A waiter brought over a fresh cup and Lugovoy invited Litvinenko to help himself.
"There was only a little left on the bottom and it made just half a cup," he said in the statement to police. "I didn't like it for some reason.... I didn't drink it anymore. Maybe in total I swallowed three or four times."
That night, Litvinenko was in his bathroom vomiting violently.
At one point, foam came out of his mouth, along with "bits of stomach with blood," he told police. "I realized that I had been poisoned."
Litvinenko spent about 20 days in a hospital, his hair falling out and his organs slowly shutting down.
It was not until the day of his death, Nov. 23, that polonium-210 was found in his body, a rare and potent radioactive substance that is difficult to detect.
Had Litvinenko not been in such good physical shape, he might have died before doctors were able to discover what killed him, doctors said.
As his life ebbed, Litvinenko gave an interview to London's Sunday Times, signed an accusatory statement that his lawyer had drawn up and insisted on posing for a now-famous photograph that shows him lying in green robes in his hospital room hooked up to machines.
Another image of Litvinenko, taken a day later when his condition had visibly deteriorated, was shown last week for the first time. It shows him lying with a feeding tube in his nose; his eyes are only faintly open and look glazed. He died the following day.
"You may succeed in silencing one man, but the howl of protest from around the world will reverberate, Mr. Putin, in your ears for the rest of your life," read a statement released after his death. "May God forgive you for what you have done, not only to me but to beloved Russia and its people."
But the Russian political elite remained unfazed.
A representative of the political party that former KGB agent Lugovoy later joined made an announcement to the Duma on the day of Litvinenko's death: "The traitor received the punishment he deserved. I am confident that this terrible death will be a serious warning to traitors of all colors, wherever they are located. In Russia, they do not pardon treachery."
Boyle is a special correspondent.