London (CNN) -- It reads like something from a spy novel. An MI6 agent known for his mathematical genius and codebreaking talent is found dead at his home, his naked body padlocked inside a large red carrying bag stowed in the bathtub.
There is no sign of a break-in or of force having been used against him. The man's Internet history betrays an interest in sex games and bondage. But DNA traces suggest other people may have been in his apartment.
The mysterious 2010 death of Gareth Williams, who worked for Britain's foreign intelligence service, is a riddle that has gripped the nation.
And at the heart of the mystery is a key question: Could Williams have zipped himself into the bag as part of a bizarre sexual fantasy? Or was the Cambridge-educated math whiz placed there by what family members have suggested are killers versed in the "dark arts" of espionage?
At Westminster Coroner's Court, a solid red-brick building across the River Thames from the headquarters of MI6 -- where fictional spy James Bond worked -- the disturbing tale of the final hours of a man known for closely guarding his privacy has unfolded in the most public of ways.
The inquest has heard that Gareth Williams was not reported missing for more than a week, despite the sensitive nature of his work, meaning many vital clues were lost to decomposition.
Meanwhile, UK media have focused on revelations about the 31-year-old's apparent interest in bondage and claustrophilia, a fetish for enclosure in very confined spaces.
Reports about the "body in a bag spy" detail how two experts spent days trying to figure out whether Williams, who was athletic and of medium height, could have contorted himself in such as way as to lock himself into the North Face holdall bag, with a key to the padlock inside.
Video provided to the court shows one of them, Peter Faulding, folding himself laboriously into an identical bag, measuring just 32 inches by 19 inches (81 by 48 centimeters), placed in a bathtub.
Faulding, who specializes in rescuing people from confined spaces, told the inquest he had tried to lock himself into the bag 300 times without success, according to the Press Association news agency. A second expert witness, also of a size and build similar to Williams, tried 100 times to re-enact the feat without succeeding.
But neither ruled out definitively the possibility Williams could have somehow done it alone. A small trace of someone else's DNA was found on the bag, helping spawn all kinds of theories -- that he was perhaps drugged by a foreign spy who then locked him in the bag, or was the victim of a kinky sexual liaison gone wrong.
The detail that the closets in Williams' central London flat contained thousands of dollars' worth of designer women's clothing and shoes, some of which had been worn, as well as women's wigs and cosmetics, added fuel to the fire of speculation.
Another revelation came from a former landlord and landlady, who told how they had once found Williams tied by his wrists to the headboard of his bed, after he shouted for help.
Williams said he had wanted to see if he could get free, landlady Jennifer Elliot told the court, but she and her husband "thought it to be more likely to be sexual than escapology," according to Press Association.
Williams was recruited into the intelligence services straight from university, working with Government Communications Headquarters before MI6. The nature of his work and questions around why his spy agency bosses took so long to raise an alert about his absence have added to the intrigue surrounding his death.
In a courtroom scene reminiscent of a spy thriller, his boss testified from behind a screen and was identified only as SIS F -- the Secret Intelligence Service being the official name for MI6.
She apologized to Williams' family for the service's failure to act sooner, but said his lifestyle choices were not a concern for the agency, suggesting it has moved on from the rigid mores of past decades, when closet homosexuality or illicit affairs opened up possibilities for blackmail.
"There is no set template for what their lifestyle should be," SIS F said of today's intelligence agents, according to the Press Association. "Individuals have lifestyle and sexual choices and sexual preferences which are perfectly legitimate."
She acknowledged that Williams had made a number of unauthorized computer searches at work but played down the significance of this fact, the agency said.
Williams was finally reported missing by a co-worker on August 23, more than a week after the normally punctilious employee had last shown up at work.
A transcript of the call to police said Williams was last spoken to on Friday, August 13, and that calls to his home number and cell phone had gone unanswered. His sister had also been unable to reach him.
The caller mentioned that Williams had "recently been pulled off of a job" and said it was unclear if he might have "taken this badly."
The family's lawyer accused MI6 of showing "total disregard for Gareth's whereabouts and safety" before he was found dead at his government-provided home, Press Association reported.
Concerns over national security have been a factor in the 20-month delay in holding Williams' inquest, and an agency more used to working in the shadows has had an uncomfortably bright light shone into its practices.
As well as adding to his family's distress, the initial delay in reporting Williams' death means forensic specialists simply cannot answer many of the most pressing questions.
Testing did not give conclusive results because the body had decomposed significantly after nine days in the summer heat of his top-floor apartment, toxicology reports posted online say.
Traces of alcohol and a chemical matching the party drug GHB were found, but both can occur naturally as part of the decomposition process, one document says. Williams was teetotal, so "even a small amount of alcohol could affect cognitive capacity," it notes.
A series of photographs provided by the Metropolitan Police show the tidy, impersonal interior of the spy's Pimlico home and the small, white-tiled bathroom where his body was found.
A bicycle parked in the hallway is a clue to Williams' more regular passion, cycling. A glimpse through the bedroom door shows a bed half-made, clothes lying on it. But little else can be gleaned from the images.
Media reports have homed in on expert testimony that despite Williams' solitary lifestyle, tiny traces of DNA from "at least two" other people were found in his apartment.
But who those visitors were and whether they hold the clue to the riddle of the agent's mysterious death are yet more questions that remain unanswered.
Williams' family, with whom he was close, deny that he was gay or had a secret, unorthodox sex life.
They believe someone else was there either when Williams died or afterward, their lawyer, Anthony O'Toole, told a hearing held before the inquest began, and they suspect some degree of expert cover-up was involved.
"The impression of the family is that the unknown third party was a member of some agency specializing in the dark arts of the secret services -- or evidence has been removed post-mortem by experts in the dark arts," O'Toole said, according to Press Association.
The inquest court is expected to give its verdict on Williams' death this week, but the final chapter of his life in the shadows may never be fully revealed to his family, or the British public.