From the U.K. Telegraph article, "Assassination fears over death of Russian oligarch Boris Berezovsky":
Boris Berezovsky was discovered dead yesterday afternoon at his home in Berkshire.
Early this morning police said they had called in specialist officers to investigate whether he had been killed by a chemical or biological agent or by radiation.
A cordon was put around his home last night after his body was discovered by a bodyguard. Reports from Russia said he was found in the bath at his house in Ascot.
Thames Valley Police said they had called in Scotland Yard and other experts and had kept the 67-year-old’s body in place as the investigation began.
Did Boris Berezovsky fall victim to an assassination ordered by Vladimir Putin?
Berezovsky, an outspoken critic of Vladimir Putin, the Russian president, had long feared for his life and had survived repeated assassination attempts — although none in recent years. He had been due to be a witness at the inquest next month into the death of Alexander Litvinenko, the former KGB spy who was murdered in 2006 after being poisoned by radioactive polonium-210 in what is believed to have been a Kremlin-sanctioned assassination.
Billionaire Boris Beresovsky was a close friend and confidante of Alexander Litvinenko, my associate who was assassinated with radioactive Polonium by the Russian secret services in 2006.
In 2005, I started up and ran the Litvinenko Chronicles at the Final Phase forum after learning that Litvinenko, a defector from the FSB who sought refuge in the U.K., had revealed what I long suspected, i.e., that al Qaeda is a Russian-run proxy for Moscow's long-standing program of international terrorism.
The number two person in the terrorist organization al Qaeda, who they are crediting with the series of explosions in London, Ayman al-Zawahiri, is an old agent of the FSB. Being sentenced to death in Egypt for terrorism and hunted by Interpol, Ayman al-Zawahiri, in 1998, was in the territory of Dagestan, where for half a year he received special training at one of the educational bases of the FSB. After this training he was transferred to Afghanistan, where he had never been before and where, following the recommendation of his Lubyanka chiefs, he at once ... penetrated the milieu of bin Laden and soon became his assistant in al Qaeda...
....I can definitely say that the center of global terrorism is not in Iraq, Iran, Afghanistan or the Chechen Republic. The terrorist infection is spread worldwide from Lubyanka Square and the Kremlin cabinet. And until the Russian special services are outlawed, dispersed and condemned, the terrorism will never stop: bombs will blow up and blood will be shed. Terrorism has no expiration date.... I would like to repeat, that all the terrorists, whom I have named, were supported by the heads of the Soviet and Russian special services - Yuri Andropov, Vladimir Putin, Nikolay Patrushev and others. These people are the main terrorists.... And until we condemn them ... global terrorism will continue.
I believe it was this revelation in particularly that cost the FSB defector his life.
Boris Beresovsky was Alexander Litvinenko's benefactor who provided the defector a home and helped produce the following documentary based upon Alexander's book: "Blowing Up Russia: Terror From Within":
In Alexander Litvinenko's book and the above documentary, the case is clearly laid out that Vladimir Putin's rise to power was paved with the blood of hundreds of innocent Russians murdered in the 1999 apartment bombings in Russia which were blamed on Chechen rebels but actually carried out by the FSB.
If you find it difficult to fathom that Russian secret services were behind the brazen assassination of Alexander Litvinenko, the 1999 apartment bombings in southern Russia and acts of international terrorism including 9/11, then I suggest you examine the following video showing Russian troops shooting dead the remaining survivors from the 2010 "crash" of of Polish Air Force Tu-154, effectively Poland's "Air Force One", that killed the political and military leadership of Poland:
Time and time again Russia's secret services have committed spectacular acts of assassination and terrorism around the world and are getting away with it because Western intelligence is downright stupid to the fact that the infamous KGB never ceased to exist with a simple name change.