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."
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 isn'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 isn'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.