An expert has said he believes a third party was present when Gareth Williams died because theories that the MI6 spy got inside a bag by himself were "unbelievable scenarios".
Mr Williams' body was found curled up naked in the padlocked holdall in the bath of his flat in Pimlico, central London, in August 2010.
Former Parachute Regiment reservist Peter Faulding told an inquest even escapologist Harry Houdini "would have struggled" to squeeze himself into the bag and lock it from the inside.
Mr Faulding, who specialises in rescuing people from confined spaces, made 300 unsuccessful attempts to lock himself inside an identical bag measuring 81cm by 48cm.
"My conclusion is that Mr Williams was either placed in the bag unconscious, or he was dead before he was in the bag," Mr Faulding said.
He suggested it would have been "very easy" to fold the dead spy's arms and place him in the holdall as long as rigor mortis had not set in.
During the forensic investigation no fingerprints were found at the scene but tiny DNA samples were discovered on the bag, their owner has never been identified.
But a second expert, William MacKay, told the inquest it was not impossible that the fitness-loving maths prodigy died without a third party present.
Mr MacKay's assistant, a yoga specialist who is of similar build to Mr Williams, carried out another reconstruction and was able to curl his body into an identical red North Face bag.
But despite more than 100 attempts, he was not able to pull the zip into position within the space, and could not lock it from the inside.
Mr MacKay told Westminster Coroner's Court: "I would not like to say that it could not be done.
"There are people around who can do amazing things and Mr Williams may well have been one of those persons."
Mr MacKay, an expert who has worked with the Army, suggested Mr Williams would have needed extensive training to have pulled off the act in pitch darkness.
Mr Williams' mountain climbing experience would have given him an advantage as it would have strengthened his fingers.
But Mr MacKay added: "It was very painful to do it. You tend to move the zip with your fingernails, straggling about. It was very frustrating, fiddly, you just can't get the thing together."
The inquest also heard how Mr Williams occasionally looked at bondage and fetish websites.
A police officer described to the coroner the findings of his work investigating Mr Williams' electronic devices.
Around half of his web browsing surrounded female fashion but he had also stored electronic images of several drag queens.
Records showed that he had researched bondage on Wikipedia and had visited bondage and fetish websites.
There was very little evidence of Mr Williams researching suffocation or experiencing confined spaces.
The inquest continues on Monday.