LONDON -- More than three years after the naked, decomposing body of British spy Gareth Williams was discovered stuffed inside a locked gym bag at the bottom of his bathtub, the mystery over his bizarre death lingers, and a police investigation has done little to clear it up.

London's Metropolitan Police said Wednesday that their investigation had found that Williams likely died in an accident with no one else involved. But the tentative conclusion, which the police hedged by acknowledging many gaps haven't been filled in, is unlikely to calm conspiracy theories surrounding the case.

Metropolitan Police Deputy Assistant Commissioner Martin Hewitt said Williams, whose remains were discovered in August 2010, was "most probably" killed in an accident, a verdict which conflicts with a coroner's inquest that concluded last year that Williams was probably killed by another person in a "criminally meditated act."

Hewitt said the police position "is that, on balance, it is a more probable conclusion that there was no other person present when Gareth died."

"But the reality is that for both hypotheses, there exist evidential contradictions and gaps in our understanding," he said.

Hewitt told reporters at Scotland Yard headquarters that his conclusion was based on the fact that investigators found little evidence of foul play in a death that has spawned a host of theories, from assassination to sexual adventure gone awry.

Williams, a cyberwarfare expert, worked for Britain's GCHQ eavesdropping service and was attached to the overseas espionage agency MI6 when he died.

Some have raised the possibility that Williams locked himself in the bag as part of a sex act gone wrong or an experiment in escapology -- the Houdini-like art of wriggling out of restraints or traps. Investigators found that he had visited bondage and sadomasochism websites, including some related to claustrophilia -- a desire for confinement in enclosed spaces.

Police concluded -- after several reenactments -- that it was possible for Williams to climb inside the sports bag and lock it.

However, police couldn't find Williams' DNA on the lock, palm prints on the rim of the bath, or footprints in the bathroom itself. The coroner, Fiona Wilcox, said that pointed to another person having taken the bag into the bathroom, noting that if Williams had been "carrying out some kind of peculiar experiment, he wouldn't care if he left any foot or fingerprints."

She was also critical in her inquest verdict of MI6, which failed to pass evidence to investigating police, and said that while it seemed unlikely that British intelligence agencies were involved in Williams' death, it was a "legitimate line of inquiry."

Hewitt said there was no evidence that the apartment had been cleaned to remove forensic traces and nothing to suggest a struggle or a break-in.

And he dismissed the idea that Britain's secretive intelligence services had carried out a coverup, noting that a total of 27 members of staff from both MI6 and GCHQ had been interviewed and that police were given full access to Williams' vetting and personnel file.

"I do not believe that I have had the wool pulled over my eyes," Hewitt said. "I believe that what we are dealing with is a tragic unexplained death."

He added that there was "no evidence to support the theory that Gareth's death was in any way related to his work."

Williams' relatives said in a statement that they were disappointed that the facts remain unclear, but still believed it was likely he had been the victim of foul play.

"We consider that on the basis of the facts known at present the coroner's verdict accurately reflects the circumstances of Gareth's death," the statement said.