Discuss as:

British spy probably was poisoned or suffocated in locked bag, expert testifies

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.

Watch World News videos on msnbc.com

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.

More world news from msnbc.com and NBC News:

Follow us on Twitter: @msnbc_world