With lots of wild theories floating around (many no doubt originating  with Russian operatives), the finger of suspicion for the Litvinenko assassination remains pointed at state organs of Russia. From The Times of London:

Intelligence services in Britain are convinced that the poisoning of Alexander Litvinenko was authorised by the Russian Federal Security Service.

Security sources have told The Times that the FSB orchestrated a "highly sophisticated plot" and was likely to have used some of its former agents to carry out the operation on the streets of London.

"We know how the FSB operates abroad and, based on the circumstances behind the death of Mr Litvinenko, the FSB has to be the prime suspect," a source said yesterday.

The involvement of a former FSB officer made it easier to lure Mr Litvinenko to meetings at various locations and to distance its bosses in the Kremlin from being directly implicated in the plot.

Intelligence officials say that only officials such as FSB agents would have been able to obtain sufficent amounts of polonium-210, the radioactive substance used to fatally poison Mr Litvinenko only weeks after he was given British citizenship.