ITV News Correspondent Paul Davies reports
Home Secretary Theresa May announced today that a public inquiry will be held into the death of the former Russian spy Alexander Litvinenko.
May said in a statement: "I very much hope that this inquiry will be of some comfort to his widow."
Litvinenko, 43, died after drinking tea that was poisoned with the radioactive substance polonium-210, in 2006.
His widow welcomed the inquiry and said she was "very pleased" by the decision.
Speaking to reporters, Marina Litvinenko said it still may take a "long time" to get to the truth.
Andrei Lugovoy, now a politician in Russia, was named by prosecutors as the main suspect in the case, but Mrs Litvinenko said she thought it was unlikely the President of Russia would change his mind and extradite him.
Alexander Litvinenko fled to the UK to claim asylum in 2000, after falling out with the Russian Federal Security Service.