Experts puzzled over U.K. spy's mystery death

(CBS/AP) LONDON - Poisoning or asphyxiation may have killed a British spy whose naked body was found locked inside a sports bag, but pathologists acknowledged Monday they can't be certain of the exact cause of his mysterious death.

Three specialists who conducted autopsies on the intelligence officer told an inquest hearing that his cadaver badly decomposed as it lay undiscovered for several days, hampering attempts to explain his death.

Gareth Williams, 31, worked for Britain's secret eavesdropping service GCHQ but was attached to the MI6 overseas spy agency when his remains were found in August 2010 at his London apartment inside the bag, and placed in a bathtub.

Mystery deepens over murdered U.K. spy

Coroner Fiona Wilcox has previously been told that MI6 colleagues failed to report Williams as missing for a week, meaning that police and pathologists lost vital chances to gather evidence.

Pathologist Benjamin Swift told the inquest that radiators had been turned on inside Williams' apartment — even though it was the height of Britain's warm summer — increasing the heat levels and accelerating the decomposition of his body.

Asked whether Williams may have been poisoned or suffocated, Swift said the options "were certainly two of the more prominent" explanations for the cryptology expert's death.

"I would never say never but those are the foremost contenders," he told the hearing.

Police have said they are not certain exactly how Williams died and have so far made no arrests, although a senior detective has told the inquest she believes that someone else must have been involved.

Ivestigators staged a re-enactment in the hopes that it would help explain how Williams wound up dead in the bathtub, CBS News' Charlie D'Agata reported (Watch report at left).

Officers have indicated Williams' death may have had links to his private life and an apparent interest in sadomasochism — possibly during a sexual encounter gone awry.

His relatives, however, insist his demise must be related to his highly secret work.

Pathologists agreed that it was most likely that Williams had climbed inside the sports bag voluntarily.

Ian Calder, who carried out a second autopsy, said Williams would have rapidly suffered from an accumulation of carbon dioxide, which "plays some considerable havoc with the chemistry of the body."

The spy would have soon been in "a situation of not being aware, of not being able to react to getting himself out of the environment," Calder said.

Pathologist Richard Shepherd, who carried out a third examination, said it was more likely that Williams "was alive when he entered the bag than that he was dead."

He said that it would have been very difficult to place Williams' dead body inside the duffel bag in the position it was found in. He was discovered in the fetal position with his arms folded across his chest.

There were also no signs that the spy had struggled to free himself.

"Were he to be alive and struggling I would anticipate there to have been injuries," Shepherd said.

Wilcox has said she expects to deliver a verdict in the case this week.