An autopsy performed on a former KGB spy killed with a radioactive poison nine years ago was the world's most dangerous post-mortem, a public inquiry into his death that began in London this week has learned, Reuters reported.

Alexander Litvinenko died Nov. 23, 2006, three weeks after ingesting a rare radioactive isotope named polonium-210 in London, a brutal killing officials say is linked to alleged deep-rooted organized crime in the heart of the Russian government.

"The murder was an act of unspeakable barbarism that inflicted on Alexander Litvinenko the most painful and lingering death imaginable," Ben Emmerson, a lawyer representing the spy's widow at the inquiry, said according to The New York Times.

"It was also an act of nuclear terrorism on the streets of a major city, which put the lives of numerous other members of the public at risk," Emmerson said.

Litvinenko, a critic of the Kremlin who defected in the '90s, was viewed as a threat because of plans to expose alleged Kremlin links to the mafia with the help of Spanish spies, Emmerson told the inquiry according to Reuters. Litvinenko reportedly told police it was Russian President Vladimir Putin who ordered his death.

The ex-spy "had to be eliminated- not because he was an enemy of the Russian State itself or an enemy of the Russian people, but because he had become an enemy of the close-knit group of criminals who surround Vladimir Putin and keep his corrupt regime in power," said Emmerson, The NY Times reported.

Litvinenko left Russia in 2000 and headed for London to seek asylum with his family. On Nov. 1, 2006 he drank a cup of tea laced with polonium-210 while at the Millennium Hotel in London's Grosvenor Square. He died 22 days later.  

A cause of death would never have been determined if it wasn't for tests conducted on Litvinenko two days before his death that found the isotope, the inquiry learned according to Reuters.

Medical examiners had to wear protective suits fitted with hoods that supplied filtered air in order to conduct the autopsy.

"It was probably the most dangerous post-mortem that's ever been conducted," Co-pathologist Benjamin Swift said according to Reuters.

British authorities at the inquiry say the suspects accused of poisoning the victim, Andrei K. Lugovoi and Dmitri V. Kovtun, brought the radioactive substance from Moscow and were with Litvinenko at the hotel the day he drank the tea.  

Both men, currently in Russia, have denied the allegations and are open to testify at the hearing, according to The NY Times.

The inquiry is expected to last at least two months.