A mystery fingerprint was found in the bathroom were the body of Russian tycoon Boris Berezovsky was discovered, an inquest heard today.
The fingerprint - found on a shower rail - was sent to crime agencies including Interpol and the FBI but has never been identified.
The revelation was made at the resumed inquest into the death of the 67-year-old political exile who was an outspoken critic of Russian President Vladimir Putin.
He was found lying dead on the floor with a ligature around his neck in the locked bathroom of his home at Sunningdale near Ascot, Berks, on March 23 last year.
A similar piece of ligature was also found on the shower rail and police said his death was consistent with hanging.
The oligarch, 67, was a close friend of KGB spy-turned-dissident Alexander Litvinenko, who died of radioactive poisoning in 2006 and had himself survived a number of assasination attempts.
However, Detective Inspector Mark Bissell, who lead the investigation into his death, told the inquest today that he believed Mr Berezovsky had taken his own life.
He said there was no evidence of a break-in or struggle, adding: "On the information and evidence obtained as part of our inquiries, we are content and believe Mr Berezovsky took his own life."
He said the death was initially treated as "unexplained" and his team carried out "proportionate" inquiries into subsequent claims that the oligarch was assassinated and that his death was faked.
Earlier the inquest heard that Mr Berezovsky became a "broken man" and often talked about killing himself after losing a multi-billion pound legal battle with Chelsea FC owner Roman Abramovich.
The former 'dynamic' Russian oligarch took anti-depressants and sought treatment for depression after losing millions in his failed High Court bid to sue Mr Abramovich for £3billion in October 2012.
Six months later the businessman was found dead by bodyguard Avi Navama.
Employees and business associates of Mr Berezovsky said his behaviour changed dramatically after he lost his court case.
Mr Navama said: "After the verdict Mr Berezovsky was very depressed.
"He used to stay inside all the time in his room."
Mr Navama told Berkshire coroner Peter Bedford that he became concerned about Mr Berezovsky when he could not raise him on March 23..
He went to the house and broke down the bathroom door to find him"lying on his back"
He said: "He looked purple. I couldn't find a pulse."
He told the inquest the tycoon had previously talked about taking his own life, once holding a knife to his arm while staying at a hotel in Israel and also threatening to jump off its terrace.
Mr Navama said: "He had said: 'Should, I jump or should I cut my veins.
"When he talked (like this) I was very worried to see him in this state. I had a very bad feeling that he might kill himself."
Mr Navama told the coroner that Mr Berzovsky's failed legal action against Mr Abramovich had been the 'trigger of the change' in his mental health.
He added:"He told me he was minus £200million that he can't pay people. He would say he's not a billionaire, he's the poorest man in the world."
Asked what had caused his boss's death, he replied: "I believe suicide."
Mr Berezovsky's legal adviser Michael Cotlic told the inquest the tycoon had spoken of suicide since October 2012 but said he had not taken him seriously.
Mr Cotlick also told how Mr Berezovsky's partner Elena Gorbunova had filed a financial claim against him which had the potential to financially ruin him.
He revealed that his friend changed his will nine days before his death, but also made several plans for meetings and appointments for after March 23.
He said: "There's only one explanation - that's suicide."
Psychiatrist Dr Saeed Islam told the hearing that Mr Berezovsky "perceived relentless pressure on him in terms of litigation and fear of losing those cases".
He said he also spoke of "enemies in Russia who were trying to destroy him and make him homeless".
Dr Islam told the inquest that Mr Berezovsky described feeling very low and told him: "I can't see a way out."
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However Mr Berezovsky's former wife, Ms Galina Besharova, said she did not believe he had killed himself.
In a statement, Ms Besharova, 55, said she spoke with her ex-husband every day, including the evening before his death.
She said: "My former husband did not plan to kill himself. I also cannot believe he would commit suicide."
Mr Berezovsky, a mathematician, gained a £3billion fortune in Russia in the 1990s when he took control of the state's newly privatised national TV station and other assets.
In 2012 he lost a High Court battle against Mr Abramovich over the ownership of Sibneft, Russia's fourth largest oil refinery.
The court judged Mr Berezovsky as an "inherently unreliable" witness, who "regarded truth as a transitory, flexible concept, which could be moulded to suit his current purposes."
The inquest was adjourned until tomorrow.