MI6 codebreaker Gareth Williams was probably killed unlawfully but the case might never be solved, a coroner has concluded.
Dr Fiona Wilcox said she was sure a third party locked Mr Williams inside the red holdall in which he was found dead.
And she 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 in her two-hour narrative verdict at Mr Williams's inquest.
"I am therefore satisfied that on the balance of probabilities that Gareth was killed unlawfully."
Dr Wilcox added that "many agencies" fell short of the required standard in handling of this case - police, MI6, LGC forensics and the Coroner's office.
She identified breakdowns in communication by her own coroner's office in ordering a second post-mortem, a DNA mix-up by forensics and the late submission of evidence by MI6 to police.
MI6 agent Mr Williams, a 31-year-old fitness enthusiast originally from Anglesey, Wales, was found naked, curled up in a padlocked holdall in the bath of his flat in Pimlico, London, on August 23, 2010.
Pathologists said he would have suffocated within three minutes if he was alive when he got inside the 81cm x 48cm red North Face bag.
Poisoning and asphyxiation are the "foremost contenders" in solving the death riddle, they say.
Bag experts have said even Harry Houdini would have struggled to lock himself in the bag while Mr Williams' family lawyer has suggested "dark arts" of the secret services were responsible.
Dr Wilcox finished her two hour narrative verdict by saying: "I am satisfied on the balance of probabilities that Gareth was killed unlawfully."
Speaking on behalf of the Williams family, solicitor Robyn Williams said: "Our grief is exacerbated by the failure of his employers at MI6 to take even the most basic inquiries as to his whereabouts and welfare, which any reasonable employer would have taken."
One of Britain's most senior spies apologised to Gareth Williams' family following the inquest, for the mix-up which saw MI6 fail to report his disappearance for a week.
Sir John Sawers, chief of the Secret Intelligence Service, expressed the "deepest condolences" of MI6 and GCHQ for the death.
In a statement delivered by MI6 lawyer Andrew O'Connor, Sir John said the service should have acted more swiftly when Mr Williams failed to turn up to work in August 2010.
Mr O'Connor said: "On behalf of the whole organisation, Sir John regrets this deeply and apologises unreservedly."
DCI Jackie Sebire has said that new lines of inquiry had come to light during Gareth Williams' inquest and that the investigation into his death is continuing.
In the video below, crime correspondent Jon Clements looks back at the inquest. Experts advise the demonstration contained in this video must not be replicated at home.