From The Australian article, "Anti-Putin former spy fights for his life":
SCOTLAND Yard is investigating a suspected plot to assassinate a former Russian spy in Britain by poisoning him with the deadly metal thallium.
Aleksander Litvinenko, who defected to Britain six years ago, is fighting for his life in a London hospital. A medical report shows he has three times the maximum limit of the odourless, tasteless poison in his body.
It is unclear how the poison was administered, but on the day he became ill he had a meal with a mysterious Italian contact.
Friends of Mr Litvinenko, a former lieutenant-colonel in Russia's Federal Security Service, are convinced he is the victim of a murder attempt by former colleagues. They regard it as similar to the plot in which a Bulgarian dissident was killed in 1978 with a poison-tipped umbrella on Waterloo Bridge in London.
One gram of thallium, a restricted substance in Britain, is enough to kill the fittest of men.
And more from Reuters: a rundown of Eastern European poisoning plots.
It's plain to see that some of the more recent poisonings are linked to the war between Russia and Chechnya; Litvinenko was investigating the murder of Russian journalist Anna Politkovskaya at the time of his poisoning. Politkovskaya was an outspoken critic of Russian President Vladimir Putin and the Kremlin's policies in Chechnya.
See also the suspected poisoning of Yuri Shchekochikhin, a Duma deputy and deputy editor of Novaya Gazeta in Moscow. Reuters reports that friends and family believed his death to be the result of dioxin poisoning. "He had been investigating the involvement of Russian security agencies in a series of apartment bombings in Moscow in 1999."
According to BBC News, Mr. Litvenenko had written a book on this subject called, Blowing up Russia: Terror from Within, which alleged "that FSB agents coordinated the 1999 apartment block bombings in Russia that killed more than 300 people."