Former Russian spy Alexander Litvinenko may have been the target of two assassination bids, an inquiry into his death by radiation poisoning has been told.
Alexander Litvinenko was allegedly poisoned by a cup of tea laced with polonium-210 in a London hotel in 2006, in the most sensational espionage case since the Cold War.
Three weeks before he died in hospital the former spy publicly accused Russian President Vladimir Putin of ordering his killing.
Russia has rejected the accusations and refused to grant extradition for the two chief suspects named by British police - Andrei Lugovoi and Dmitri Kovtun - over the poisoning of Litvinenko on 1 November that year.
Lawyer Robin Tam told the inquiry in London traces of radiation showed there may have been a previous poisoning when the three met in the offices of a London private security company, Erinys, two weeks earlier on 16 October.
"One of the most significant things that the evidence suggests is that Litvinenko was poisoned with polonium not once but twice," he told the inquiry at the Royal Courts of Justice, which was attended by Litvinenko's widow Marina.
Mr Tam also showed the inquiry diagrams of the Erinys boardroom showing heavy contamination on a section of the table and a chair, as well as on the spout of the teapot from which Litvinenko drank at the Mayfair hotel.
He said the heaviest contamination in the boardroom and the teapot was "off the scale" at in excess of 10,000 counts per second (cps). Normal background radiation is around 0.5 cps.
While much of the attention has been on Lugovoi, a former KGB bodyguard who has since become a member of parliament in Russia, Mr Tam's comments focused more on the role of Mr Kovtun.
He said a friend of Mr Kovtun's from Germany - who will remain anonymous and will be identified only as "D3" - is set to testify that the Russian told him he had poison and needed a contact for a cook to kill Litvinenko.
"Kovtun said that he had a very expensive poison and that he needed the cook to put the poison in Litvinenko's food or drink," he said.
Mr Kovtun also allegedly told his friend at a meeting on 30 October that Mr Litvinenko was "a traitor with blood on his hands," he added.
The inquiry will probe claims of Russian state involvement in a death which shocked the world and Mr Tam said "there are a number of strands of evidence relating to possible Russian state responsibility for Litvinenko's death."
But he indicated that he would also look at other theories, including the possibility that he may have been killed by Britain's MI6 foreign intelligence service, the Russian mafia or exiled oligarch Boris Berezovsky.
Speaking to Russia's TASS news agency, Mr Lugovoi on Tuesday dismissed the inquiry as "a farce".
It will examine classified documents, referred to only as material from "HMG" (Her Majesty's Government) and parts of the final report may have to be redacted to exclude sensitive intelligence information.
The inquiry's chairman, judge Robert Owen, said on Tuesday that the public hearings would last for two months and that he expected his report to be ready by the end of the year.
"The issues to which his death give rise are of the utmost gravity and have attracted worldwide interest and concern," Owen said.
Under English law, such inquiries are not trials and only establish the facts of a case in public but do not result in convictions.
The spy's wife Marina Litvinenko told AFP the inquiry was the best she could hope for short of a trial for Mr Lugovoi and Mr Kovtun.
"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."
Her lawyer Ben Emmerson on Tuesday said Litvinenko had been investigating alleged ties between Putin and organised crime.
Alexander Litvinenko served in the KGB during Soviet times and then in its successor agency, the FSB, when Putin led it before becoming president in 2000.
In 1998, he and other FSB agents gave a press conference in Moscow accusing the agency of a plot to kill Berezovsky, who helped bring Putin to power but later turned against him.
Mr Litvinenko was tried for abuse of power and, although acquitted in 1999, he fled Russia and was granted asylum in Britain.