The British government Tuesday announced plans for a wide-ranging public inquiry into the 2006 death of poisoned ex-Russian spy Alexander Litvinenko.
The decision, which comes at a time of rising tensions with Russia, means investigators can look into whether the Russian state played a role in Litvinenko's demise.
"The death of Alexander Litvinenko was an appalling crime and we want to see those responsible prosecuted through the courts," a government spokesman said.
The statement said the inquest would be "entirely independent" from the government and would be chaired by Robert Owen, who has been acting as coroner in an inquest into the death. That inquest has been barred from considering secret evidence about the possible role of the Russian state, but the public inquiry will have more scope.
Home Secretary Theresa May announced the inquiry in a written statement.
The decision drew immediate praise from Marina Litvinenko, the spy's widow, who had long called for a judicial inquiry to establish the facts surrounding her husband's agonizing death.
She said she was "relieved and delighted" by the decision. The message, she said, was that "no matter how strong and powerful you are, truth will win out in the end."
Two Russians have been named as prime suspects, but they deny involvement and remain in Russia.
The case led to a hardening of relations between Britain and Russia that has gotten more severe in recent days because of the downing of a civilian airliner over the conflict zone in eastern Ukraine.
Litvinenko, who had become a strong critic of the Kremlin, died in London after drinking tea laced with polonium-210.
Until now, the British government has declined to conduct a full scale inquiry. Britain's High Court ruled earlier this year that the government had to reconsider its decision.