Timeline: Litvinenko death case
Who was Alexander Litvinenko?
At the inquiry into the Russian ex-spy's death, Mrs Litvinenko revealed her husband acted as a "consultant" to a British intelligence service. She could not confirm which agency but the BBC understands it was MI6.
The court also heard that Mr Litvinenko believed Vladimir Putin had links to organised crime in his earlier career.
Mr Litvinenko came into contact with the now-Russian president in 1998 when Putin was head of the FSB, Russia's secret service. Mrs Litvinenko told the inquiry:
Mrs Litvinenko did not know details of Mr Putin's alleged criminal connections but said that during the period of Putin's deputy mayoralty, St Petersburg was known as "the criminal capital of Russia".
It is the first time Mrs Litvinenko has given evidence at the public inquiry into the death of Mr Litvinenko, who died after drinking tea laced with radioactive polonium at a hotel in London in 2006.
Mrs Litvinenko also told the court that after a 1998 press conference - during which her husband revealed he had been asked to murder businessman Boris Berezovsky - he confided in her that he believed he would soon be killed or arrested.
He feared their whole family would be condemned, she said, which led to their decision to leave Russia.
On landing at London's Heathrow Airport, Mr Litvinenko apparently approached a police officer and said: "I'm a KGB officer and I'm asking for political asylum." After being granted asylum, Mr Litvinenko began to receive support payments from Mr Berezovsky - who Mrs Litvinenko described as a friend - while he spoke out against the Russian government and wrote for Chechen websites.
Mr Berezovsky later stopped the payments, and in 2004 Mr Litvinenko began to act as a paid consultant for MI6 on organised crime, receiving £2,000 a month for information. His widow said Mr Litvinenko also worked for Spanish security services on organised crime investigations.
It is already known that Mr Litvinenko revealed he was asked to carry out a murder, but on Monday the court heard new details about his career and how he got to know the Russian businessman Mr Berezovsky.
Mr Litvinenko joined the secret service - then the KGB - towards the end of the Cold War and later, after it had been renamed the FSB, he became part of an anti-terrorist unit.
He next joined a specialist unit targeting organised crime, through which he met Mr Berezovsky. Mr Berezovsky amassed a fortune in the 1990s following the privatisation of state assets after the collapse of Soviet communism. He emigrated to the UK in 2000 and was granted political asylum in 2003 on the grounds his life would be in danger in Russia.
He was found dead at his Berkshire home in 2013. An inquest into his death returned an open verdict.
The barrister representing the Litvinenko family claimed earlier in the inquiry that Mr Litvinenko was murdered for attempting to "expose the corruption" at the heart of Vladimir Putin's "mafia state". The two Russian men identified by the Met Police investigation as suspects, Andrei Lugovoi and Dmitry Kovtun, have denied any involvement and remain in Russia.