• Gareth Williams’s body was found in a bag at his London flat five years ago
  • Spy illegally hacked into secret data on former U.S. president Bill Clinton
  • Personal voicemail messages left by the spy were deleted after he died

The British spy whose body was found padlocked inside a bag in his flat had illegally hacked into secret data on former U.S. president Bill Clinton, it has been revealed.

Gareth Williams, 31, was discovered in a holdall in the bath at his London home five years ago this month, but the mystery surrounding his death has never been solved.

Today, it has been revealed the spy had dug out a guest list for an event Clinton was due to attend as a favour for a friend.

The hack breached Mr Williams’ security clearance and this sparked anger among MI6 bosses as tensions rose with U.S. security services over the spy’s transatlantic work, The Sun on Sunday has reported.

A source said: ‘The Clinton diary hack came at a time when Williams’ work with America was of the most sensitive nature.

‘It was a diplomatic nightmare for Sir John Sawers, the new director of MI6 at the time.’

The paper has also reported that voicemail messages Mr Williams, a maths genius and expert cryptographer, left for family and friends were deleted shortly after his death.

Earlier this month, it was revealed that detectives who investigated the mysterious death believe he was murdered and that his killers then broke back in through a skylight to cover their tracks.

The claim centres on the revelation that part of the forensic equipment placed in the flat after the body was found was moved – despite the fact the building was under armed police guard.

The theory supports his family’s suspicions he was murdered by ‘agents specialising in the dark arts of the secret services’.

Mr Williams had been working with the American National Security Agency in Washington before returning to London, where he underwent training and was sent on active operations.

The exact nature of his work remains a closely guarded secret, but sources claim he dealt with equipment that tracked the flow of cash from Russia to Europe.

The technology enabled MI6 to follow money trails from bank accounts in Russia to criminal European gangs. One theory is that Mr Williams had disrupted a mafia ring closely linked to the Russian state.

Cars registered to the Russian Embassy were spotted near his Pimlico flat just days before his body was discovered on August 23, 2010.

Mr Williams was last seen alive on August 15 – a Kremlin car was seen near his property that day.

Other lines of inquiry, also dismissed by the Metropolitan Police at the time, were that he was killed by MI6 or American agents after stumbling on sensitive data, or because he threatened to make secret intelligence public.

There were also claims Mr Williams may have been killed by a lover during a bizarre sex game.

Coroner Dr Fiona Wilcox, who heard the 2012 inquest into his death, criticised MI6 for failing to report that the spy had been missing for a week, saying this caused extra suffering for his family and led to the loss of forensic evidence.

The delay, for which MI6 apologised, also meant a Home Office pathologist was unable to find a cause of death.