The death of a British spy -- whose body was found in a padlocked bag in a bathtub in his London apartment -- may never be explained but was likely a criminal act, the coroner investigating the case said Wednesday.

The coroner, Fiona Wilcox, said that it was a "legitimate line of inquiry" that other spies were involved in the death of Gareth Williams, 31, a member of the U.K.'s Secret Intelligence Service, known as MI6, according to a report in The Guardian newspaper.

Wilcox said the spy was likely killed either by suffocation or poisoning in a "criminally meditated act."

She also said she did not think Williams' passing interest in sexual bondage was behind his death, The Telegraph newspaper said.

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The body of British spy Gareth Williams was found in a bag in his bathtub.

Wilcox said that if Williams, a math prodigy who worked as a code breaker, had got into the bag by himself, foot and fingerprints would have been found around the bath, the paper reported. 

"It is unlikely this death will ever be satisfactorily explained," she said, according to the media reports.

Spy death inquiry looks at bondage link

The coroner also said the large number of women's clothes in the apartment did not show that Williams was a transvestite, The Telegraph noted. The case, she said, had produced in "endless speculation but little evidence."

However, she added that the circumstances of the death "immediately raised the possibility of foul play," according to the Guardian.

UK cops close to arrest over British spy found dead in a bag?

Williams' body was found in his apartment in Pimlico, London, in August 2010.

Metropolitan Police / Reuters

A combination of still photographs taken from video shows a man trying to lock himself in a holdall in this undated image received from the Metropolitan Police in London on April 27.

A forensic pathologist, Benjamin Swift, testified Monday that Williams probably suffocated or was poisoned, saying a precise cause of death could not be established because the body had decomposed. Williams died more than a week before his body was found.

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Other experts have said that it was highly likely that another person, or two, were involved.

The case has spawned any number of conspiracy theories that Williams may have been assassinated by foreign agents or terrorists.

MI6 has said it believes his death was  nothing to do with his work.

The Associated Press contributed to this report.

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Andrew Winning / Reuters file

Ian and Ellen Williams and Cerri Subbe, the mother, father and sister of British MI6 agent Gareth Williams, left Westminster Coroner's Court in London on April 23.

Gareth Williams, the British cyberspy who was found dead in a padlocked duffel bag, probably suffocated or was poisoned, a forensic pathologist testified Monday.

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Williams' body was found in the bag in the bathtub of his apartment in London in August 2010. The unusual of his death — Williams, 31, a math prodigy who worked as a code breaker for the British spy service MI6, was discovered naked and showing no signs of a struggle — has transfixed Britain as details of Williams' transvestism and sexual fantasies have emerged.

Speaking at an official inquest into Williams' death in August 2010, the pathologist, Benjamin Swift, said the precise cause of death couldn't be pinpointed because the body was badly decomposed after having been in the bag for more than a week before it was found, The Guardian reported. But he said  asphyxiation or poisoning were the "foremost contenders."

Spy death inquiry looks at bondage link

Other experts have testified that it was highly likely that another person, or even two, was involved in the case, citing the near-impossibility of Williams' being able to lock himself into the bag.

UK cops close to arrest over British spy found dead in a bag?

That has spawned any number of conspiracy theories that Williams may have been assassinated by foreign agents or terrorists. But MI6 said it believed his death had nothing to do with his work or that it had covered it up.

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British spy Gareth Williams was “dead or unconscious” and was almost certainly placed in a sports bag by another person, an inquiry into his death in London was told Friday, it is reported.

Expert Peter Faulding tried to re-create the code-breaker’s bizarre death by trying to climb into a bag inside a bathtub and lock it himself 300 times. He failed every time, according to a report of the day’s inquest evidence in the Daily Telegraph.

Faulding said the task would have eluded even escapologist Harry Houdini.

UK intelligence officer: No cover-up in 'spy in the bag' case

He said he believed a third party was present, describing theories that Williams got inside the bag unaided as "unbelievable."

Video footage of Faulding attempting to re-create the death was shown to the inquest.

Police discovered the naked decomposing body of the 31-year-old spy padlocked inside a red sports bag in the bathtub of his flat in London in August 2010.

The strange circumstances surrounding Williams’ death have prompted a number of theories, and police eventually concluded he had been playing an auto-erotic sex game that went badly wrong.

Earlier this week, the inquest heard from Williams’ former landlady, who once found the spy in bed with his hands tied to the headboard wearing nothing except boxer shorts.

Faulding, a former Parachute Regiment reservist who specializes in rescuing people from confined spaces, was unable to lock himself inside an identical bag in the bath, according to a Press Association report.

"I couldn't say it's impossible, but I think even Houdini would have struggled with this one," he said, according to the PA. The expert added: "My conclusion is that Mr. Williams was either placed in the bag unconscious, or he was dead before he was in the bag."

He also raised the idea the bag was deliberately placed in the bath so “bodily fluids” could drain away.

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LONDON - There was "no evidence" to suggest that British intelligence services were part of a cover-up after one of their own was found naked and decomposing inside a locked duffel bag in his London apartment, an intelligence officer said on Thursday.

"Witness F" gave evidence to the inquest -- which are held when deaths are deemed violent or unnatural -- in the August 2010 death of MI6 officer Gareth Williams from behind a screen, BBC News reported.

MI6, Britain's foreign intelligence agency, is roughly equivalent to the Untied States' CIA.

The denial came on the same day that one of the code-breaker's relatives shrieked and brought proceedings to a halt while listening to details of a series of missteps that allowed for the spy to lay in his bathroom undiscovered for a week, the Telegraph reported.

UK cops close to arrest over British spy found dead in a bag?

The relatives walked out of the inquest in tears during Witness F's evidence, the BBC reported.

Their lawyer Anthony O'Toole said the agency showed a "total disregard for Gareth's whereabouts and safety."

Williams, 31, was a math prodigy working as a codebreaker at Government Communications Headquarters (GCHQ), the state eavesdropping service. 

Williams' family became increasingly upset during the four days of proceedings as it became clear that his absence did not spark any concern, despite the sensitive nature of his job, according to reports.

Witness F, a senior intelligence officer, told the inquest that MI6 was "profoundly sorry" for the delays, which had made it more difficult for the family to "come to terms with his dreadful death," the newspaper reported.

A detective told the inquest on Tuesday that a "third party was involved in that padlock being locked, and Gareth being placed in the bag."

Spy death inquiry looks at bondage link

The inquest has also been told that Williams, who was single and intensely private, would not have let a stranger into his flat, and that he would not have given his keys to anyone apart from close family.

There were no signs of a break-in or indications of foul play.

Small amounts of unidentified DNA were detected on the bag.

On Wednesday, the inquest heard that years earlier Williams had been found tied to his bed and unable to free himself.

Williams had shouted out for help in the middle of the night when he was living in an annex of the home of his then-landlady Jennifer Elliot in Cheltenham, western England.

Mystery couple sought in UK cyberspy's bizarre death

Elliot and her husband found Williams dressed only in boxer shorts with his hands tied to the headboard of the bed. He told her that he had been just "messing about," trying to see "if I could get myself free," the Telegraph newspaper reported.

In a written statement, Elliot said it was likely "to be sexual rather than escapology," the paper added.

Williams later took up a three-year assignment at the headquarters of Britain's foreign intelligence service MI6, whose offices are on the banks of the River Thames in central London.