By Olivia Harris
ASCOT, England (Reuters) - Specialist police with nuclear and chemical training gave the all clear at the British home of former Russian oligarch Boris Berezovsky on Sunday, a day after the fervent critic of Russian President Vladimir Putin died in unclear circumstances.
Once known as the "godfather of the Kremlin", the former billionaire powerbroker helped Putin rise to the top before falling out of favor himself and fleeing to Britain in 2000.
Police said the 67-year-old's death was "unexplained" and sent radioactive, biological and chemical experts to do tests as they tried to piece together Berezovsky's final hours.
Berezovsky had survived assassination attempts, including a bombing that decapitated his driver, and said he feared for his life after he became one of Putin's fiercest critics, repeatedly calling for him to be forced from office.
He was also a friend of Alexander Litvinenko, the former Russian spy who was poisoned with radioactive material in London in 2006, a murder that strained diplomatic ties between Britain and Russia.
However, friends said the man who personified the ruthless post-Soviet era of massive wealth and political scheming was depressed, had lost his fortune and may have committed suicide.
Others suspected he could have had a heart attack after the stress of losing a $6 billion court case to Chelsea Football Club owner Roman Abramovich. British newspaper reports said his security guard found the body in the bath.
Police stood guard outside Berezovsky's mansion, an imposing French-style property with a swimming pool and lake in Ascot, a few miles from Queen Elizabeth's Windsor Castle, 25 miles west of London. Inside, detectives were carrying out a thorough search of the house.
"The CBRN (chemical, biological, radiological and nuclear) officers found nothing of concern in the property and we are now progressing the investigation as normal," Superintendent Simon Bowden, of Thames Valley Police, said in a statement.
In what is thought to have been his last media interview, given in London on Friday, Berezovsky, said he was sorry he had left Russia to live in self-imposed exile in Britain and was struggling to see the "point of life".
"I do not know what to do. I am 67 years old. And I do not know what to do next," he was quoted as saying in the Russian edition of Forbes magazine. "I've lost meaning. The point in life."
Putin's spokesman said Berezovsky, seen by Moscow as a criminal who should stand trial for fraud and tax evasion, had written to the president asking for forgiveness - a suggestion dismissed by one of the oligarch's friends.
"Berezovsky sent Vladimir Putin a letter he wrote personally, in which he acknowledged that he had made many mistakes, asked Putin's forgiveness for these mistakes and appealed to Putin to help him return to his homeland," said Putin's spokesman Dmitry Peskov.
A friend of Berezovsky's in London, Andrei Sidelnikov, told Reuters the idea that he wrote a letter to Putin was "complete nonsense".
"He was a sane person and he understood that he would never be able to return under Putin's regime, for political reasons," Sidelnikov said.
A former mathematician who made millions selling luxury cars in Russia, Berezovsky became part of the inner circle of former president Boris Yeltsin and helped forge Putin's career.
The pair fell out soon after Putin's election in 2000 and Berezovsky left for Britain where he denounced his former ally as a corrupt "bandit" surrounded by former KGB agents.
Berezovsky was humiliated in 2012 when he lost a legal battle with former partner Abramovich, over shares in Russia's fourth biggest oil company.
Some associates said he had struggled with the cost of losing to Abramovich, estimated at the time as more than $100 million. Berezovsky had kept a low profile since the defeat and was rarely seen in public.
"He had no money, he had lost it all. He was unbelievably depressed," Tim Bell, a public relations executive who was one of his closest British advisers, told the Sunday Times newspaper. "It's all very sad."
(Writing by Peter Griffiths in London; Additional reporting by Maria Golovnina and Guy Faulconbridge in London and Thomas Grove, Maria Tsvetkova, Alexei Anishchuk in Moscow; Editing by Louise Ireland)