The inquest into the death of MI6 officer Gareth Williams has been told that poisoning or asphyxiation were the 'foremost contenders' in causing his death.
Dr Benjamin Swift, who performed the first post mortem on Mr Williams' body, had concluded the cause of death was 'unascertained'.
He found "a bruise on left forearm, graze on left elbow, graze on right elbow, graze to right eye socket
Dr Swift said there were no signs of sexual assault or poisoning, or any 'significant internal or external traumatic injuries'.
There was no sign of any 'offensive, defensive or restraint' injuries on the body either.
While saying he did not want to speculate on the cause of death, Dr Swift said poisoning or asphyxiation were "possibilities", but stressed he could not prove or disprove either.
The body was extensively decomposed, something that had been exacerbated by the radiators in the flat being turned on.
The inquest has heard from two other pathologists, both of whom said they agreed with the 'unascertained' cause of death finding.
Dr Ian Calder said Gareth's body would take up 60 litres space on the bag, leaving 25 litres of oxygen inside.
Carbon dioxide would have a big effect on anyone in the bag, causing headaches, confusion and drowsiness. This could explain why Gareth made no attempt to get out of the bag, if he wasn't already dead, said Dr Calder.
It would have taken two to three minutes before 'toxic hypercapnia' took effect, he said.
He agreed, however, that someone conscious when they went into the bag would be aware they were getting weak and could try to get out.
Dr Richard Shepherd, who performed the third autopsy, insisted the cause of death was 'unnatural', and that poisoning and suffocation were possible factors.
He cast doubt on the idea that someone could have escaped from the bag, stating "there was no possibility" of escape once the lock was put on.