Russian tycoon Boris Berezovsky.
A fierce critic of President Vladimir Putin, the former mathematician was found dead at his home in Britain on Saturday.
British police said the death was unexplained and began an investigation on Sunday, using officers trained to detect chemical, biological, radiological and nuclear tampering.
Sixty-seven-year-old Berezovsky, once a member of the Kremlin's political elite, helped Putin rise to power, only to become his sworn enemy and flee into exile in Britain.
Associates say the businessman may have committed suicide or suffered a heart attack after losing a 6 billion US dollar court case to football club owner, Roman Abramovich.
Some residents in the Russian capital Moscow seemed largely unaffected by news of Berezovsky's death.
(SOUNDBITE) (Russian) MOSCOW RESIDENT ANDREI, SAYING:
"Who cares? Really. The man has not lived in Russia for so many years, and in fact he was thrown away from here. Who cares? I'm
