The widow of former KGB agent Alexander Litvinenko has said she believes the Russian authorities could have been behind his murder.
Mrs Litvinenko said her husband had been a "very good friend"
Marina Litvinenko, 44, told the Mail on Sunday: "Obviously it was not Putin himself, of course not."
But she said what President Putin "does around him in Russia makes it possible to kill a British person" in Britain.
Two Metropolitan Police officers have tested positive for traces of radioactive substance polonium-210.
Mrs Litvinenko said she had confidence UK police would find her husband's killer, but would not help Russia's planned probe.
She told the Mail on Sunday Russian authorities had not yet been in touch with her.
"I do not think I will help them with their investigations," she said.
"I can't believe that they will tell the truth. I can't believe if they ask about evidence they will use it in the proper way."
Mr Litvinenko died in a London hospital on 23 November after being poisoned by polonum-210.
The Metropolitan Police said two of the 26 police officers closely involved in the subsequent inquiry had tested positive for traces of the substance.
It said the polonium traces were "relatively small" and were "below defined safety limits".
Both officers are being monitored by health specialists.
Mr Litvinenko's widow said he had alienated the FSB
Mrs Litvinenko also told the Mail on Sunday her husband's last words to her were: "Marina, I love you so much."
She also said she and "Sasha", as her husband was known to family and friends, had been convinced he would recover.
"Even until the last day, and the day before when he became unconscious, I thought he would be okay...
"We had been talking about bone-marrow transplants and looking to the future."
Mrs Litvinenko said the couple's 12-year-old son had found his father's death "very difficult", but he had been trying to comfort his mother.
Friends of Mr Litvinenko believe he was poisoned because of his criticisms of the Russian government, but the Kremlin has dismissed suggestions it was involved in any way.
After Mr Litvinenko's death Kremlin spokesman Dmitry Peskov said: "We don't consider it possible to comment on the statements accusing the Kremlin because it is nothing but sheer nonsense."
Russia's foreign intelligence service has also issued a statement denying any involvement.
Mrs Litvinenko told the Sunday Times she had decided to speak out after some "completely untrue" reports suggested her husband was a man of dubious character.
She told the paper he had been an honest man and a crime fighter rather than a spy.
She said her husband's public claims about his former employers at the FSB, Russia's secret police, had alienated them.
Speaking on BBC One's Breakfast AM, Vladimir Bukovsky, a Soviet dissident and a close friend of Mr Litvinenko's, said it was "clear" the Russian authorities were behind the poisoning.
He said a law had been passed in Russia earlier this year enabling the president "to eliminate his particular enemies anywhere, including outside of Russian territory".
Mr Bukovsky said the definition of "enemies" included anyone engaged in libellous criticism of the Russian administration.
He added: "Right as the law was passed the number two in the Kremlin hierarchy the Minister of Defence Sergei Ivanov made a statement saying that the list of potential targets was already composed.
"Now what else do you need? Then followed the murder of Anna Politkovskaya and Alexander Litvinenko and there will be others to follow."