The widow of Alexander Litvinenko, Marina Litvinenko (R) and a solicitor (L) arrive outside the Royal Courts of Justice, in London, Britain, 27 January 2015. EPA/FACUNDO ARRIZABALAGA

For nearly a decade, Marina Litvinenko has been trying to conclusively prove who killed her husband -- and why.

His death was like something out of a spy thriller. Alexander Litvinenko, an ex-KGB officer, was poisoned in 2006 after drinking a cup of tea laced with a radioactive substance. As he lay dying in a hospital in London, Litvinenko accused Russian President Vladimir Putin of ordering his murder. His killing attracted global attention.

On Thursday, a major British inquiry concluded that Putin “probably” ordered her husband’s death.

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, Marina won a legal battle in the high court after she challenged the British Home Secretary Theresa May’s refusal to hold a public inquiry. May had cited “international relations” as one of the factors 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,” her lawyer, Ben Emmerson, said in an interview.

He said that 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 that the public inquiry was held at all.

Marina “has demonstrated a quiet determination to establish the true facts of her husband’s death that is greatly to be commended,” Owen wrote.  

Marina, a former dancer from Moscow, met Alexander 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 the U.K., where Alexander was an outspoken critic of the Kremlin.  

Speaking to reporters on Thursday, Marina 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, the lawyer, said that Marina 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 the U.K. before “the final fall” of Putin, but said that they will 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, 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.”