Police baffled by mysterious death of millionaire Russian supergrass

A supergrass who was helping prosecutors uncover a multi-million pound money laundering scheme used by corrupt officials in Russia has died in mysterious circumstances outside his Surrey home, i can reveal.

Alexander Perepilichnyy, a wealthy businessman who sought sanctuary in Britain three years ago after falling out with a powerful crime syndicate, collapsed outside his mansion on a luxury private estate on the outskirts of Weybridge. He was only 44 and in seemingly good health.

i has learnt that Mr Perepilichnyy was a key witness against the "Klyuev Group", an opaque network of corrupt Russian officials and underworld figures implicated in a series of multi-million pound tax frauds and the death in custody of the whistle-blowing Moscow lawyer Sergei Magnitsky. He is the fourth person linked to the scandal who has died suddenly.

Surrey Police said that a post mortem examination of Mr Perepilichnyy had proved "inconclusive" and further tests were being carried out to try to establish a cause of death.

Officers were called to his home on a cul-de-sac shared with seven multi-million pound properties on 10 November, but the Russian was declared dead 30 minutes later. Surrey Police would not confirm suggestions that he had been out running.

Evidence provided by Mr Perepilichnyy detailed how a number of tax officials from Moscow became obscenely wealthy in the aftermath of a tax fraud against a British investment fund and used Swiss based bank accounts to purchase luxury properties in Dubai and Montenegro.

Earlier this year Swiss prosecutors opened an investigation into a number of accounts at Credit Suisse after Hermitage Capital Management forwarded them a dossier of evidence implicating the Russian officials. "Perepilichnyy was the guy who brought all the evidence they needed to open the investigation," said one source. "He brought with him records of shell companies, Credit Suisse accounts, property transactions."

Hermitage Capital was once one of the largest foreign investors inside Russia until it became the victim of a $230m (£144m) tax fraud scheme.

Corrupt officials from Russia's powerful Interior Ministry conspired with tax officers to steal corporate seals from Hermitage Capital following a police raid and apply for a series of tax rebates using those seals. Complicit courts and tax offices signed off on the deal and the money was transferred into a bank which was liquidated shortly afterwards.

Hermitage hired Mr Magnitsky to investigate the scam and he publicly named a number of key Interior Ministry officials who he believed were involved. Days after going public he was arrested by the same men he had accused and was held in prison for a year. He died in November 2009 after being refused vital medication following months of brutal treatment.

Thanks to campaigning by Bill Browder, CEO of Hermitage Capital, the case has become an embarrassment for Russia and a lightning rod for anger over official corruption.

The British hedge fund declined to comment on Mr Perepilichnyy's death. A source with knowledge of the investigation in Switzerland confirmed that he had been providing prosecutors and Hermitage Capital with evidence on the corrupt tax officials.