No evidence of nuclear or chemical contamination has been found at the home of Russian billionaire Boris Berezovsky who was found dead yesterday. 

Specialist police officers spent the night examining his home in Berkshire in England in search of possible leads. But his death is being treated as unexplained. 

Journalist and former Russian Government advisor Alexander Nekrassov says the tycoon had become depressed after losing his money and leaving his homeland to go into exile after becoming critical of Vladimir Putin's regime at the Kremlin.