I have asked my lawyers to petition HM Coroner to hold a full inquest into the murder of my husband, Alexander Litvinenko. Only a review of the evidence in an open, independent court in Britain will get to the truth about who poisoned his tea with radioactive polonium-210 on November 1, 2006, as well as how and why.

I do this against the wishes of the Scotland Yard and David Miliband, the Foreign Secretary, who both told me that making the evidence public would prejudice a criminal trial of the chief suspect, Andrei Lugovoy, whom the UK is trying to extradite from Russia. But after waiting for 15 months I have come to the conclusion that Mr Lugovoy, a former KGB agent, will never be extradited. So I respectfully reject their argument. I cannot wait for another ten years for a slim chance that their approach would bear fruit.

I should emphasise that I hold no grudge against the police or the British Government; I am eternally grateful to them for identifying and naming the suspect, and then slapping Russia with an extradition request, which, even though it has not been successful, has squarely put the blame for Alexander's death at the Kremlin's door. However, this is not good enough for me. If I cannot get justice, then at least I need the full truth.

While the British authorities are constrained by due process and could do nothing more than repeat futile extradition pleas, the Kremlin has embarked on a propaganda campaign designed to divert the blame from itself. It wants to destroy the reputation of Alexander, a former member-turned-critic of the FSB, Russia's security service, and to discredit the allegations he made that the Kremlin was behind the assassination of the journalist Anna Politkovskaya and a series of apartment bombings in 1999 that was blamed on Chechen separatists.

Officials at the highest levels at the Kremlin have insinuated that my husband's friends in London killed him “in order to smear Russia”. In a scam worthy of the old KGB, a fringe American journalist was invited to Moscow for an interview with Russian prosecutors, who showed him the British extradition papers - the ones that I am not allowed to see. His “conclusion” - that my husband poisoned himself while smuggling radioactive material for terrorists - was published in a third-rate New York newspaper and then trumpeted in Russia as an American-sourced report. I have to protect my husband's good name from such dirty tricks. A full inquest would put an end to these kind of smear campaigns.

I fully trust the British police when they say that they have an ironclad case against Mr Lugovoy. But I am not the one who needs convincing. It is the Russian people who need to know. Mr Lugovoy professes his innocence, and none other than President Putin has cast him as a victim of “British colonialism” on national TV. Millions of Russians believed these claims, and now Mr Lugovoy has been elected to the Russian Parliament for an ultra-nationalist party that slavishly supports the Putin line. In the meantime, the evidence against him remains sealed in London. I cannot afford for it to remain there for ever. I need a full inquest to show both men for what they are: a murderer and his patron.

I am frustrated by the fact that Mr Lugovoy is the sole focus of the British indictment. With all the evidence against him, he did not have a motive or access to polonium-210. Somebody sent him and gave him the poison, which must have been produced, dosed, tested and packaged by someone else. Experts say that the Avangard nuclear plant in Russia is the only place where they make polonium-210, and that security there is so tight that it could not have been taken away without an official order. They also say that “nuclear forensic analysis” must have established the origin and the production date of the batch that killed my husband. I want the polonium report to be read in the coroner's court. Then perhaps Russia would have to explain how the material produced in its most secure facility ended up in Mr Lugovoy's suitcase in a London hotel room.

People tell me that disclosure of the whole truth would further damage British relations with Russia. Even a hint of Russian official complicity would put the British Government into an awkward position; after all, killing a British citizen in London with a radiological weapon is an act of war or of state-sponsored terrorism or both. What should the UK then do? How would Russia retaliate? Tens of billions of pounds of investments are at stake. Geopolitical balance is, too. Don't make yourself into a problem, I am told.

To this I answer: I am not the problem. The problem is the people who sent Mr Lugovoy to London with a weapon of mass destruction in a suitcase. If they went to such lengths to get rid of my husband, imagine what they would do if their larger interests are at stake. Denying this would not make the problem go away; it would only make it worse.

Russia will soon have a new president. Dmitri Medvedev is not tainted by the crimes of the previous regime. He says that he wants to bring the rule of law to Russia. He has the power to cleanse Russia of the people who killed my husband, but I am not sure that he has the will. If he dares not, he will become their hostage. But if he dares, he will need evidence, which is sealed in the Scotland Yard files. An inquest in London holds a huge promise for Russia; it might just tip the balance between the bright and the bleak outcome.

But the most important reason for wanting this inquest to take place is that I owe it to my husband. Many years ago in Moscow, just before his first arrest, he told me: “Marina, if something happens to me, you would go around the world and tell people what happened and why.”

I did not believe him then. He repeated it on his deathbed in London. He wanted me to go out and alert the people to the evil that rules in the Kremlin. I am doing this for him.

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