http://news.yahoo.com/s/nm/20070615/...nko_spies_dc_3

The fsb has launched an investigation and concluded that litvenko with berezovsky were both spies and that the british or berezovsky had litvenko killed in order to frame the kremlin.

Or....anti-Putin elements within the Russian government did it to discredit Putin. He has been smacking down the oligarchs, they would have good reason to do all this.