LONDON (AFP) - The most sensational spy tale since the Cold War landed in a London court on Tuesday as inquiry hearings began to examine alleged Russian state involvement in the radiation poisoning death of Alexander Litvinenko.
The former agent with Russia's FSB security service, who was doing work for Britain's MI6, was killed with Polonium-210 and the case was referred to at the time as the world's first act of nuclear terrorism.
British police believe that the radioactive isotope was stirred into Litvinenko's tea by Andrei Lugovoi and Dmitri Kovtun, two acquaintances visiting from Moscow, at a meeting in a London hotel on November 1, 2006.
He died three weeks later and a statement in his name accused President Vladimir Putin, saying that "the howl of protest from around the world will reverberate, Mr Putin, in your ears for the rest of your life".
"The issues to which his death gives rise are of the utmost gravity," the inquiry's chairman Robert Owen said at the start of Tuesday's hearing.
Owen said closed-doors hearings would examine intelligence material on "the issue of Russian state responsibility for Mr Litvinenko's death".
The hearings are set to last around two months and Owen said his report would be out by the end of the year.
Owen said Lugovoi and Kovtun had been invited to testify via video-link but Russian authorities have already ruled out any participation with the inquiry.
- 'Political provocation' -
Britain's Daily Telegraph newspaper reported at the weekend that communications between London and Moscow intercepted by the US National Security Agency pointed to Russian state involvement.
The BBC also reported that the killing may have been the third attempt on Litvinenko's life.
At the time, Putin rejected the accusations of Russian state involvement as a "political provocation".
There are other theories about who may have killed him, given Litvinenko's investigative work in other European countries including Italy and Spain and his specialisation in researching organised crime.
During an earlier inquest, a lawyer for Litvinenko's widow, Marina, said he had been working for the MI6 foreign spy service - receiving monthly payments of £2,000 (S$4,053) and reporting to a contact called "Martin".
Owen was the coroner in the inquest but did not have the power to examine intelligence documents. He lobbied for an inquiry to be able to do so.
Under British law, such inquiries establish the facts of a case in public but do not result in convictions.
- 'Defend his name' -
Britain announced the inquiry in July 2014, just days after the downing of Malaysian Airlines flight MH17 over eastern Ukraine - a tragedy blamed on Russia's involvement in the conflict in the region - in what was seen as a way of punishing Russia.
Marina Litvinenko told AFP the inquiry was the best she could hope for since Russia has refused to grant extradition requests for Lugovoi and Kovtun to stand trial.
"My struggle has been for the facts to be made public," she said, adding: "This is the last thing I can do for him, defend his name.
"The discussion will no longer be about whether to believe or not, but about facts. My struggle has been for the facts to be made public."
Litvinenko served in the KGB during Soviet times and then in its successor agency, the FSB. In 1998, he and other FSB agents gave a press conference in Moscow accusing the agency of a plot to kill Boris Berezovsky, an oligarch who helped bring Putin to power but later turned against him.
Litvinenko was tried for abuse of power and although acquitted in 1999 he fled Russia, apparently through Georgia and Turkey with a fake passport.
He was later tried and sentenced in absentia on different charges that his family says, like the abuse of power allegations, were invented to silence him.
Litvinenko was granted asylum in Britain and later became a British citizen.
A veteran of the 1994-1996 Chechen war, he later converted to Islam after befriending exiled Chechen separatist leaders.
He was buried in a London cemetery with Muslim rites in lead-lined coffin to prevent radiation leakage.