(Photo: Reuters/Eddie Keogh)The British Houses of Parliament in central London.

A mafia whistle-blower has been found dead in his mansion in Britain. The Russian businessman had been helping Swiss prosecutors in a case against a powerful fraud syndicate connected to a Russian mafia scandal.

Alexander Perepilichny, 44, has been found dead in unexplained circumstances, according to Reuters on Thursday. Perepilichny had fled to Britain three years ago to seek refuge. He had been helping a Swiss investigation into a Russian money-laundering scheme, and had allegedly been helping compile evidence against corrupt officials.

Previously he had helped with evidence against those linked to corruption in the high profile 2009 case of anti-corruption lawyer Sergei Magnitsky. Perepilichny is now the fourth person to have died in mysterious circumstances who had been connected to the Magnitsky scandal.

It is reported that Perepilichny died not far from his home in Surrey in South London earlier this month. A police spokesperson in Britain has said, "It is being treated as unexplained. A post-mortem examination was carried out which was inconclusive. So further tests are now being carried out."

Perepilichny was said to have been in running clothes when his body was found after dark near his home at the top of a hill.

Liam Walsh, a 24-year-old local chef, has told Reuters, "He wasn't breathing. We had to get him on the back and start doing CPR (first aid). He was probably dead for a while."

A former employer of Magnitsky, William Browder, has said Perepilichny connected with the Magnitsky investigation in 2010 and worked with Swiss prosecutors. Browder said, "Alexander Perepilichny approached us in 2010 as a whistleblower with evidence about the complicity of a number of Russian government officials in the theft of $230 million which Sergei Magnitsky had uncovered."

"He provided us with copies of many of the original bank documents. In January 2011, Hermitage filed an application to the Swiss authorities seeking an investigation. It was announced in March that the Swiss prosecutor's office opened an investigation and froze the assets in a number of accounts."