Poisoning and asphyxiation are the "foremost contenders" in the sports bag death riddle of MI6 spy Gareth Williams, an inquest heard today.
Mr Williams was probably suffocated or killed by a poison which disappeared in his system during decomposition, pathologist Benjamin Swift said.
Dr Swift said his post-mortem examination was hampered by levels of heat within the bag after radiators were mysteriously turned on in Mr Williams's top floor flat in the middle of summer.
But under questioning at Westminster Coroner's Court, Dr Swift said poisoning or asphyxiation such as suffocation were "probably rather than possibly" to blame.
Dr Swift said the two causes of death "were certainly two of the more prominent" beliefs as he conducted examinations.
When family lawyer Anthony O'Toole asked if there were any other possible causes of death, Dr Swift replied: "I would never say never but those are the foremost contenders."
There were no injuries indicating Mr Williams had struggled to get out of the bag, in which he was found naked and in the foetal position, the pathologist added.
But no tablet deposits were found in his system and there was no bruising consistent with strangulation.
Dr Swift said he believed Mr Williams would have died shortly after his last known movements on August 15.
Williams was found dead in a Government flat in Pimlico in August 2010.
After excelling at university at mathematics, Williams worked as a cipher and codes expert at the Government listening station, GCHQ.
Williams was then seconded to work at the Secret Intelligence Service headquarters in Vauxhall, London.
CCTV captures Williams entering Holland Road Tube Station on the 14th August 2010.
Caught on CCTV at Holland Road Tube Station the same day.
Seen the next day on CCTV in Hans Crescent, London
His body was found in a holdall in this Pimlico flat on the 24th of August 2010.
Williams' funeral was attended by Sir John Sawers, head of SIS.
Screengrab from a video reconstruction showing a yoga specialist trying to lock himself in a sports holdall unaided
Screengrab from a video reconstruction showing a person trying to close the zip and padlock themselves in a sports holdall unaided