A British spy was probably killed unlawfully but the case might never be solved, a coroner said today.
Fiona Wilcox said she was sure a third party locked M16 codebreaker Gareth Williams inside the red holdall in which he was found dead.
She also criticised the 21-month investigation as she said it was unlikely the riddle "will ever be satisfactorily explained".
"The cause of his death was unnatural and likely to have been criminally mediated," she said at Mr Williams's inquest.
"I am therefore satisfied that on the balance of probabilities that Gareth was killed unlawfully."
Mr Williams' family criticised his employers at MI6 afterwards for their response to his death, saying "our grief was exacerbated" by it.
His sister looked on as Dr Wilcox told a packed Westminster Coroner's Court that "on the balance of evidence" he was probably alive when he was put in the bag.
Dr Wilcox said it remained a "legitimate line of inquiry" that the secret services were involved in Mr Williams's death.
But she said "there was no evidence to support that he died at the hands of" spies as the inquest drew to a close.
She ruled that "it would appear that many agencies fell short" during the inquiries into his death.
Despite a 21-month police inquiry and seven days of evidence, "most of the fundamental questions in relation to how Gareth died remain unanswered", she said.
Mr Williams was suffocated by carbon dioxide, possibly as an onset of a short-acting poison, the coroner suggested.
She dismissed speculation that Mr Williams died as a result of some kind of "auto-erotic activity", also denying there was any evidence to suggest claustrophilia - the love of enclosed spaces - was of any interest to him.
"I find on the balance of probabilities that if he had got into the bag and locked himself in, he would have taken a knife in with him," she said. "He was a risk assessor."
MI6 apologised for failures in raising the alarm about his disappearance earlier as Dr Wilcox said several factors hampered inquiries.
Breakdowns in communication by her own coroner's office in ordering a second post-mortem examination, a DNA mix-up by forensics and the late submission of evidence by MI6 to police were singled out for blame.
Mr Williams, a 31-year-old fitness enthusiast originally from Anglesey, North Wales, was found naked, curled up in the padlocked holdall in the bath of his flat in Pimlico, central London, on 23 August, 2010.
Pathologists said he would have suffocated within three minutes if he was alive when he got inside the 32-inch by 19-inch bag.
Bag experts said that even renowned escapologist Harry Houdini would have struggled to lock himself in the bag, while Mr Williams's family lawyer has suggested the "dark arts" of the secret services were behind the mystery.
Police recovered no evidence of a third party being present and have no suspects in their inquiry.
