Getting there was a long, arduous journey, with Marina Litvinenko fighting tirelessly. At one point, she took the British Government to court.
Two years ago, she won a legal battle in the high court after she challenged British Home Secretary Theresa May's refusal to hold a public inquiry. May had cited "international relations" as one factor in the decision not to go forward.
Launching the challenge was financially risky. If Litvinenko lost, she would have had to pay for the Government's legal fees.
"She literally had to put her house on the line. Not to pay her own lawyers - we were acting pro-bono - but to pay the Government's lawyers if she lost. Luckily we won," said her lawyer, Ben Emmerson.
He said she was a "remarkable woman" who had made it clear from the very beginning that she would not be able to get on with her life until she had found the truth about her husband's death.
Marina's son Anatoly, who lost his father when he was 12, recently told the BBC, "I don't think many people would be able to do what she's done."
Robert Owen, a former high court judge who led the inquiry, wrote in the inquiry report that it was because of the dogged efforts of Marina Litvinenko that the public inquiry was held at all.
She "has demonstrated a quiet determination to establish the true facts of her husband's death that is greatly to be commended", Owen wrote.
Marina Litvinenko, a former dancer from Moscow, met Litvinenko in 1993 when he was investigating a case that involved her friends. The following year, they had a son and were married. They would later claim asylum in Britain, where Alexander Litvinenko was an outspoken critic of the Kremlin.
Speaking to reporters on Thursday, Marina Litvinenko called on the British Government to expel Russian intelligence officers and to impose sanctions and travel bans on specific individuals, including Putin.
So far, Government officials have announced they have seized the assets of the chief suspects in the case, Andrei Lugovoi and Dimitry Kovtun - a gesture some commentators have said was largely symbolic.
Emmerson said Marina Litvinenko was "unsatisfied" with the British Government's initial response, but added they were still waiting to see what further actions will be taken.
He has acknowledged that there is little chance of Lugovoi and Kovtun standing trial in Britain before "the final fall" of Putin, but said that they would continue to press for a strong response.
British Prime Minister David Cameron would be "craven" if he failed to act following "an assassination akin to nuclear terrorism" on the streets of London, Emmerson said.
Standing outside the Royal Courts of Justice on Thursday night, Marina Litvinenko nonetheless welcomed the conclusions of the mammoth investigation.
"I am of course very pleased," she said. "The words my husband spoke on his deathbed when he accused Mr Putin of his murder have been proved true."
Key points
• Judge Robert Owen cited abundant evidence that Andrei Lugovoi and Dmitry Kovtun placed radioactive polonium-210 in Alexander Litvinenko's tea at a London hotel on November 1, 2006. He died on November 23.
• Owen concluded there is a "strong probability" the poisoning came under the direction of Russia's FSB spy agency, and that the operation was probably approved by then-FSB chief Nikolai Patrushev and by President Vladimir Putin.
• Putin spokesman Dmitry Peskov denounced the inquiry as a "quasi-investigation" that would "further poison the atmosphere of our bilateral relations" with Britain.
• British Prime Minister David Cameron said the evidence in the report of a state-sponsored killing is "absolutely appalling", and Britain summoned the Russian ambassador for a dressing-down and imposed an asset freeze on Lugovoi and Kovtun.
• Interpol has issued notices calling for their arrest, although Russia refuses to extradite them.
• British-Russian relations have been chilly, but the report comes as the countries are cautiously trying to work together against Isis (Islamic State) in Syria, and neither wants a major new rift.
