Alexander Litvinenko, former Russian agent, may have been poisoned twice

Former Russian agent Alexander Litvinenko was poisoned with radioactive polonium not once but twice, a British judge was told Tuesday, as an inquiry opened into the slaying one lawyer called an act of nuclear terrorism ordered by Moscow.

Ben Emmerson, attorney for Litvinenko's widow, said the KGB spy turned Kremlin critic was the victim of an "assassination by agents of the Russian state."

He said the 2006 killing "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."

Litvinenko, who had become a Britain-based critic of the Kremlin, fell violently ill on Nov. 1, 2006 after drinking tea with two Russian men at a London hotel. He died three weeks later, aged 43, of "acute radiation syndrome."

Litvinenko's extraordinary killing and his deathbed statement that he was poisoned on orders from President Vladimir Putin soured Russian-British relations for years. Judge Robert Owen, who is overseeing the inquiry, said the issues raised by the death "are of the utmost gravity."

Moscow denies involvement

No one has ever stood trial for Litvinenko's killing. Britain and the dead man's family have accused Russia of involvement. Moscow denies the claim, and has refused to extradite the two men identified by Britain as the prime suspects.

Robin Tam, the inquiry's legal counsel, said in an opening statement that the inquiry was not a trial whose job was to determine guilt but that it would try to follow the evidence wherever it led.

Outlining key evidence, Tam said that detectives had found "a large number of positive traces" of the radioactive isotope polonium-210 in London locations visited by Litvinenko and the two suspects: Dmitry Kovtun and former KGB agent Andrei Lugovoi. Ingesting a tiny amount is enough to kill.

Tam said the inquiry would hear evidence that Litvinenko "was poisoned with polonium not once, but twice" and the poisoning "met with at least some success" on both occasions. Litvinenko complained of feeling ill a couple of weeks before he was hospitalized, after an earlier meeting with Kovtun and Lugovoi.

The inquiry would also hear from a witness who says Kovtun asked him if he knew a London cook who could put a "very expensive poison" in Litvinenko's food, Tam said.

Kovtun and Lugovoi have strongly denied involvement in Litvinenko's death. The judge said they have been invited to give evidence to the inquiry by video link from Russia.

Litvinenko's widow, Marina, has said she hopes the inquiry will reveal the long-buried truth about her husband's death.

Intelligence evidence to be heard in secret

The investigation first stalled because Russia refused to hand over the suspects, then because British authorities would not disclose secret intelligence evidence. Under the terms of the inquiry, that evidence will be heard, but in secret.

Public hearings at London's Royal Courts of Justice are due to last until April, and Owen said he hoped to publish his findings by the end of the year.

• Marina Litvinenko's2012 interview with CBC's As It Happens

Owen has already said that he has seen secret British government material that "established a prima facie case that the Russian state was responsible" for Litvinenko's death.

Tam said the inquiry would look at Litvinenko's role in Russia's first Chechen war and his later sympathy for the Chechen cause, and would hear evidence that the ex-spy converted to Islam on his deathbed.

He said the inquiry would look at Litvinenko's relationships with the late Russian oligarch Boris Berezovsky and with slain journalist Anna Politkovskaya, and his increasingly vocal criticism of the Kremlin.

Tam said the judge would need to ask himself whether such actions would have made Moscow authorities regard him "as an irritant, or worse."

He said the inquiry also would consider whether British security agencies, Berezovsky, underworld figures or Chechens could have been responsible or even whether Litvinenko's death was an accident or suicide.

Emmerson said these theories were "absurd." He said Litvinenko was killed after exposing links between the Kremlin and organized crime that showed Putin to be "a common criminal dressed up as a head of state."

Emmerson said that when all the evidence had been heard, "Mr. Litvinenko's dying declaration will be borne out as true."

"The trail of polonium traces leads not just from London to Moscow but directly to the door of Vladimir Putin's office," he said.