A British coroner has recorded an open verdict in the death of Boris Berezovsky, saying he could not prove the Russian oligarch had meant to take his life.
The Kremlin insider-turned-critic, 67, was found lying on the floor of the locked bathroom of a mansion in Ascot, near London, with a ligature around his neck in March 2013.
The two-day inquest heard that Berezovsky was a "broken" man and regularly talked about suicide after losing a legal battle against Chelsea owner Roman Abramovich.
But it also heard evidence from his daughter Elizaveta saying he thought he might have been poisoned, while a medical expert said the tycoon could have been strangled.
Coroner Peter Bedford said "contradictory" evidence meant he could not prove beyond all reasonable doubt that the businessman either took his own life or was unlawfully killed.
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"I am not saying Mr Berezovsky took his own life, I am not saying Mr Berezovsky was unlawfully killed," Bedford said.
"What I am saying is that the burden of proof sets such a high standard it is impossible for me to say."
Members of the Berezovsky family declined to comment on the verdict as they left the court in Windsor.
Berezovsky was a key power broker in the Kremlin but fled to Britain when he fell out with President Vladimir Putin and was granted asylum.
The tycoon's bodyguard, who found Berezovsky's body, told the inquest that his employer had been depressed after losing a STG3 billion ($A5.42 billion) damages claim against fellow oligarch Roman Abramovich in 2012.
The coroner said: "It is clear to me and the witnesses I have heard that it had a significant effect not only on his finances but also on his mental health."
Although there were suggestions that Berezovsky - who had survived at least two assassination attempts - was murdered, police did not find any evidence of foul play.
Berezovsky was a friend of Russian dissident Alexander Litvinenko, who was murdered with radioactive polonium in London in 2006, and had been due to testify at Litvinenko's own inquest.
In the immediate aftermath of Berezovsky's death, experts from Britain's Atomic Weapons Establishment attended the scene but found no evidence of radiation, the inquest heard.
* Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.
