CCTV images show Gareth Williams in a lift at Holland Park Tube station in August 2010
A British spy whose naked body was found padlocked in a bag in his bathtub was probably unlawfully killed, a coroner concluded Wednesday.
But it is "unlikely" that the full circumstances of the death in 2010 of Gareth Williams, a high-flying codebreaker with the MI6 external intelligence agency, will ever be explained, coroner Fiona Wilcox added.
"I am satisfied on the balance of probabilities that Gareth was killed unlawfully," Wilcox said at the end of a dramatic inquiry into the death.
She said she was "satisfied" that "a third party moved the bag containing Gareth into the bath" of his London flat.
MI6 chief John Sawyers apologised to the family after the inquest, admitting that his service should have reported the 31-year-old's absence from work more quickly.
The inquest heard that experts could not determine how the gifted mathematician had died because his body had been decomposing for a week by the time it was discovered.
London's Metropolitan Police said after the hearing they were pursuing new lines of inquiry raised by the inquest, after the coroner had criticised their handling of the case.
"I have always been satisfied that a third party may have been involved in his death, and the coroner has confirmed that in her findings," said Detective Chief Inspector Jackie Sebire.
"The inquest has raised several new lines of inquiry and the investigation will now refocus," she added. "I urge anyone who knew Gareth or who had contact with him to search their conscience and come forward."
Pathologists said in evidence that Williams likely died from poisoning or suffocation.
The hearings focused on whether he could have locked himself into the red North Face holdall as part of a lone sex act, after examination of his computer showed he had visited bondage websites.
But the coroner said it was "highly unlikely" that Williams could have got inside the bag alone and observed that the surfaces around the bathtub were strangely clear of any evidence.
"If Gareth had been carrying out some kind of peculiar experiment, he wouldn't care if he left any foot- or fingerprints," Wilcox concluded.
The inquest heard last week from experts who had failed to padlock themselves into bags identical to Williams' holdall, despite several hundred attempts.
One expert said escapologist Harry Houdini "would have struggled" to pull off the feat.
Wilcox ruled out the possibility that Williams' apparent interest in bondage had an impact on his death, and observed: "I would have expected much more Internet activity to have been recovered."
The coroner also questioned leaks of details about Williams' private life, adding: "I wonder if this was an attempt by some third party to manipulate the evidence."
Police found women's clothing worth about Â£20,000 ($32,400, 24,500 euros) in the flat as well as make-up, but Wilcox said there was no evidence to suggest Williams was a transvestite.
There was some suggestion that his interest in female footwear could have been of a sexual nature, but this was not particularly unusual, she argued.
The coroner said she did not have enough evidence to give a definitive verdict of unlawful killing, and instead delivered a two-hour narrative verdict listing all the possibilities.
After the inquest, Williams' family hit out at the failures of MI6 to raise the alarm after the spy went missing, saying their grief had been "exacerbated" by the agency's inaction.
The family also hit out at the secret services, saying they were "extremely disappointed" by their "reluctance and failure" to make relevant information available to the inquiry.
MI6 failed to report Williams' disappearance for a week, while police told the inquest they had not been able to examine some of Williams' possessions including nine memory sticks because his bosses said they were irrelevant.
Sawyers said MI6 expressed its "deepest condolences" to Williams' family for their "tragic loss".
"Lessons have been learned, in particular the responsibility of all staff to report unaccounted staff absences," he added.