British police said Friday there were no suspicious circumstances in the death of a Russian whistleblower who was a key witness against Russian officials accused of stealing $230 million from a London hedge fund in a money laundering scheme.

Alexander Perepilichny's body was discovered in November 2012 outside his rented house in southern England. He had been in possession of documents that allegedly blew the lid off a massive Russian tax fraud involving dirty money being funneled into Swiss bank accounts.

There were fears the 44-year-old had been poisoned, and two autopsies carried out in November failed to establish the cause of death.

Det. Chief Inspector Ian Pollard said he is satisfied that following extensive inquiries and "a full and detailed range of toxicology tests, there is no evidence to suggest" third-party involvement in Perepilichny's death.

Police said Friday that toxicology samples taken from both autopsies came back clear and that the matter has been formally passed to the coroner for an inquest.

The force acknowledged frustration about the length of time it took to complete the inquiries, stressing that it was important to rule out foul play and put to rest speculation he had been poisoned -- a possibility floated given the suspicious deaths of other Russians in the U.K.

The most prominent case was the death of Alexander Litvinenko, the former KGB agent who died in London in 2006 after being contaminated with radioactive Polonium 210.

Perepilichny had been aware of reports that his life had been threatened, and was cooperating as a whistleblower in relation to the same money laundering scheme that was being investigated by Sergei Magnitsky, a Russian lawyer hired by the London-based hedge fund Hermitage Capital, who died in a Moscow jail in 2009 amid torture claims.

Perepilichny had approached Hermitage officials in 2010 and provided extensive documents on the alleged scheme. Bank statements, company registry documents and ownership records of offshore companies were then passed onto Swiss investigators.

Russian criminal gangs are alleged to have helped in the $230-million money laundering scheme. Perepilichny is one of four men linked to the investigation who have died young.