LONDON (REUTERS) - Pathologists examining the body of former KGB spy Alexander Litvinenko, poisoned with a rare radioactive isotope nine years ago in London, carried out the world's most dangerous autopsy ever on his body, an inquiry into his killing heard on Wednesday.
They also said they would probably never have discovered the way in which he had died had unusual tests not been carried out just before his death.
British police say Kremlin critic Litvinenko died three weeks after drinking tea poisoned with polonium-210 at the plush Millennium hotel, which they believe was administered by two Russians Andrei Lugovoy and Dmitri Kovtun.
At its opening at London's High Court on Tuesday, the inquiry was told Mr Litvinenko had told police that Russian President Vladimir Putin had personally ordered his death.
His widow's lawyer said this was to partly to cover up Kremlin links to the mafia, which the former spy was going to help Spanish intelligence to expose.
Russia and the two suspects have repeatedly rejected any involvement in the death.
Mr Litvinenko's health deteriorated rapidly after his meeting with Lugovoy and Kovtun on Nov 1, 2006, and he died later that month having suffered multiple organ failure.
The inquiry was told "an inspired hunch" by police led them to bring in atomic scientists who found Mr Litvinenko tested positive for alpha radiation poisoning two days before he died.
Lead pathologist Nat Cary said without that, the cause of death would not have been discovered in a post-mortem, adding he was unaware of any other case of someone being poisoned with alpha radiation in Britain, and probably the world.
Co-pathologist Benjamin Swift told the inquiry: "It was probably the most dangerous post-mortem that's ever been conducted."
Those involved had needed to wear two white protective suits with specialised hoods fed with filtered air.
One of Britain's top nuclear scientists, identified only as A1, told the inquiry only a tiny amount, nanograms to micrograms, of polonium would be fatal.
Tests had shown traces of polonium in parts of a ceramic teapot from the Millennium Hotel, including its spout, which were "off the scale", she said.
However, she said the purity of the polonium they had found meant it was impossible to determine where it had been made.
The controversy generated by Mr Litvinenko's killing plunged Anglo-Russian relations to a post-Cold War low.
As ties improved though, Britain rejected holding an inquiry in 2013, but then, as the Ukraine crisis unfolded, the government changed its mind last July although it said the political Ukrainian situation was not a factor.
Mr Ben Emmerson, the lawyer for Mr Litvinenko's widow, Marina, said the police's main suspect Lugovoy had given an interview to Russian radio on Tuesday denouncing the inquiry as a "judicial farce".
"When the situation in Ukraine had kicked off and the UK's geographical interests had likely begun to change, they decided to dust off the mothballs and commence these proceedings," Lugovoy said according to Mr Emmerson.