The UK has evidence the Russian state was involved in the murder of Alexander Litvinenko, who was working for MI6 when he died, a coroner has heard.
The pre-inquest review was told the former KGB spy had been hired by MI6 for a number of years and was also working with Spain to investigate the Russian mafia shortly before his death.
Mr Litvinenko was poisoned with polonium-210 after allegedly drinking tea at a meeting with two former Russian colleagues - Andrei Lugovoy and Dmitry Kovtun - in London's Millennium Hotel in November 2006.
Russia has refused to extradite the prime suspects, Mr Lugovoy and Mr Kovtun, both of whom deny involvement.
The hearing revealed for the first time that Mr Lugovoy - now a Russian MP - was double-crossing his government and helping with an investigation into the Russian mafia's links with the Kremlin and Russian President Vladimir Putin.
Hugh Davies, counsel to the inquest into Mr Litvinenko's death, said assessments of confidential material submitted by the British Government had "established a prima facie case as to the culpability of the Russian state in the death of Alexander Litvinenko".
After the hearing, Mr Litvinenko's wife Marina said she was pleased the alleged involvement of the Russian government in her husband's murder would now be considered by the inquest.
"We've been saying this many times but this is the first time this question has been raised in court," she said.
"I appreciate all that was done today and I'm looking forward to any decision, which will be taken by the coroner after today's hearing."
It was also heard that Mr Litvinenko would regularly meet with an MI6 handler, named only as Martin, in central London and was paid by both the British and Spanish secret services into a joint bank account he held with his wife, the hearing was told.
Ben Emmerson QC, representing Mrs Litvinenko, said the inquest should also consider whether MI6 failed in its duty to protect against a "real and immediate risk to life".
Mr Davies said assessments of confidential material that was submitted by the British Government showed there was no evidence to suggest the UK was involved in the poisoning of Mr Litvinenko or that it failed to take necessary steps to protect him.
The evidence also ruled out the involvement of other parties, including friend Boris Berezovsky, Chechen-related groups and the Spanish mafia, he added.
Mr Emmerson said Mr Litvinenko had been asked by MI6 to work with the Spanish secret service and the inquest should consider whether "detailed risk assessments" were carried out.
He had been due to travel to Spain with Mr Lugovoy shortly before his death to provide intelligence in the Russian mafia investigation, Mr Emmerson said.
The investigation was looking at links between Russian political parties, organised crime and arms trafficking, he added.
Neil Garnham QC, representing the Home Office, told the hearing he could "neither confirm nor deny" whether Mr Litvinenko was employed by British intelligence services.
The Russian Federation has now indicated its wish to become an interested party in the inquest, which is to be held on May 1.
The inquest will be held before High Court judge Sir Robert Owen, who has been appointed assistant deputy coroner.
Mr Litvinenko died three weeks after he was poisoned - after authorising the release of a photo showing the devastating impact of radiation poisoning on his body.