Russian President Vladimir Putin “personally ordered” the killing of Alexander Litvinenko, the inquiry into the former spy’s death has heard.
Ben Emmerson QC, for Mr Litvinenko’s family, said in his closing statement that Russian state responsibility had been proven “beyond reasonable doubt”.
Mr Litvinenko’s widow Marina said she believed her husband’s “murderers and their paymasters” had “been unmasked”.
But the Kremlin told the BBC it did not trust the inquiry.
Dissident Mr Litvinenko, 43, drank tea containing a fatal dose of radioactive polonium during a meeting with suspects Dmitry Kovtun and Andrei Lugovoi in London in 2006.
The Kremlin wanted Mr Litvinenko dead and provided the poison used to kill him, Mr Emmerson alleged.
Scientific evidence proves Mr Kovtun and Mr Lugovoi killed the former spy, he added.
Mr Emmerson told the inquiry Mr Putin was an “increasingly isolated tinpot despot” and a “morally deranged authoritarian”.
He said the Russian president and his allies are “directly implicated in organised crime”.
Mr Putin’s “personal cabal” are “willing to murder those who stand in their way”, Mr Emmerson added.
He said: “If the Russian state is responsible, Vladimir Putin is responsible.
“Not on some analogical version of vicarious liability but because he personally ordered the liquidation of an enemy who was bent on exposing him and his cronies.”
The QC said Mr Kovtun had failed to appear before the inquiry because he would be unable to explain the evidence against him.
Mr Kovtun said in March that he wanted to testify, but failed to appear by videolink.
Speaking outside the Royal Courts of Justice after the closing statements, Mrs Litvinenko said she believed “the truth has finally been uncovered”.
She said her husband had “vowed to expose corruption” in the Russian Federal Security Service and the “highest echelons of power in Russia”.