Moscow ( CNN ) As Alexander Litvinenko lay dying on his bed in a London hospital in November 2006 , he was in no doubt as to who was to blame for his imminent death . The 43-year-old former Russian agent turned Kremlin critic pointed his finger directly at Vladimir Putin , then as now , Russia 's strongman president . `` You may succeed in silencing me but that silence comes at a price , '' Litvinenko said in the statement from his deathbed . `` You may succeed in silencing one man but the howl of protest from around the world will reverberate , Mr. Putin , in your ears for the rest of your life . '' READ MORE : Did Russia put polonium in spy 's tea ? It 's an allegation the Kremlin has never really managed to shake off . Officials have always dismissed the charge as `` nonsense , '' but suspicions linger . The Kremlin 's case is n't much helped by the compelling evidence against it . The poison used to kill Litvinenko is a rare radioactive isotope , polonium-210 . It occurs naturally , but scientists say the high concentrations found in the Litvinenko case indicate production at a nuclear reactor , or perhaps a particle accelerator . The kinds of facilities , in other words , controlled by a state . Russia is n't the only country capable of producing polonium-210 . But the radioactive trail left by the substance -- literally a trail of detectable radioactive material -- was traced across London , while three British Airways aircraft that had flown a number of routes , including London to Moscow , were reported to be contaminated with small traces of an unnamed radioactive substance . The two prime suspects in the poisoning , Andrei Lugavoi and Dmitry Kovtun , are Russian nationals . Both are former agents of the Russian security services . But both deny involvement and the Russian government refuses to extradite either to Britain to face trial . Litvinenko had many enemies . He was a former agent of the Russian Federal Security Service , the FSB , the post-Soviet successor of the feared KGB . His last job at the agency was heading up its anti-corruption department . It was in the chaos of the 1990s , in the aftermath of the collapse of the Soviet Union that may well have brought him into conflict with ruthless colleagues . After leaving the FSB , he blamed the service for orchestrating a series of apartment bombings in Russia in 1999 that left hundreds dead and led to Russia 's invasion of Chechnya later that year . Litvinenko 's wife also claimed her husband was in the pay of the British security services after moving to the UK in 2000 . All or any of the above may have been sufficient reason to kill a man seen by his former FSB colleagues as a traitor . There are some questions that even the public inquiry now underway in Britain may never be able to answer . Why , for instance was polonium-210 chosen to kill Litvinenko ? It would have been a costly and complicated task to produce the quantity used in the murder . A bullet would have been much cheaper . Perhaps the killers hoped it would not have been detected by British investigators . Or perhaps they wanted to send a message , pointing the police towards an executioner they knew would never be held to account ? But the biggest question of all is whether the killing was ordered by the state , or was the work of rogue elements within it . Perhaps only President Putin , himself a former KGB agent , has the answer to that .
Alexander Litvinenko died in 2006 after being poisoned by radioactive material . The Russian government has denied any involvement and blamed the British for his death. Russian President Vladimir Putin was accused by the ex-spy of being behind it .