Bondage link to dead spy mystery

Investigators said the 31-year-old codebreaker was immersed in the capital's thriving gay nightlife and had repeatedly visited extreme bondage websites though no bondage equipment was found in his flat.

He also had a secret passion for fashion and hoarded unworn women's designer clothes worth 15,000 in his wardrobe alongside several wigs.

The labels included Stella McCartney, Christopher Kane, and Louboutin and were in their original boxes or wrapping paper. Williams had also enrolled in two fashion design courses at Central Saint Martins College, in Clerkenwell, London, in 2009 and 2010.

Police said it would have been impossible for the dead man to lock himself in the holdall where his naked body was found on August 23. They also revealed forensic evidence indicates other people were in his Pimlico flat who they have been unable to trace.

But police said it is impossible to say whether Mr Williams was already dead when he was put in the bag or died from suffocation once zipped inside.

Detective Chief Superintendent Hamish Campbell said the spy's secretive private life probably holds the key to his death and that a "small sub-group of the community" may know something about his final moments but police cannot trace them.

Speaking at New Scotland Yard yesterday, Mr Campbell said: "We are very sure that someone else was in that flat. We want to know the circumstances when you would leave somebody in that position, by accident or design. Maybe, by explaining to the public, someone will think: 'I get it and I can explain."'

Mr Williams, of Anglesey, North Wales, was found by police at his top-floor flat in Alderney Street, Pimlico, on August 23.

Police believe he died in the early hours of Monday August 16 and he was last seen the previous day returning from a shopping trip to Harrods.

His decomposing body was in a large North Face holdall sealed by a travel-style Yale padlock through the zip fasteners. The keys were inside, under his body.

An expert found the temperature inside the waterproof holdall would have risen to 30C within three minutes and Mr Williams would have suffocated within half an hour.

The mathematics prodigy worked as a cipher and codes expert for GCHQ, the Government listening station but had been on secondment to MI6. The death sparked a frenzy of speculation as a battery of post-mortem tests and a huge police inquiry failed to determine how he died.

Detectives revealed the new details of their investigation yesterday as they announced an inquest will examine the case next year.

They said disclosing the "embarrassing, hurtful and distressing" information was necessary to provoke a greater public response.

Det Chief Insp Jackie Sebire, who has led the inquiry, released e-fit images of a Mediterranean couple who were seen visiting Mr Williams' block in late June or early July.

The couple, in their 20s, were buzzed through the communal entrance by another resident and suggested they had been given a key by "Pierre Palo" and were on their way to his flat.

Mr Williams had recently returned from a fly-drive holiday to the West coast of America and may have combined the trip with work at the National Security Agency in Washington DC.

Detectives have quizzed colleagues at GCHQ, MI6 and the NSA who said the dead man was an intensely private individual who kept a low key presence at work social occasions while enjoying cycling and keeping fit in his own time.

Mrs Sebire said police have been unable to trace any sexual partners, male or female, and the only people who had flat keys were Mr Williams and the letting agent.