03/05/2012 03:21 BST

Gareth Williams Death: MI6 Members To Be DNA Tested

Members of the secret services are expected to come under scrutiny as detectives redouble their efforts to solve the mystery of spy Gareth Williams's death.

MI6 came under fire as a coroner said she was sure a third party locked the code-breaker inside the red holdall in which his naked body was found in his bathtub.

Police strongly suspect a member of MI6 or GCHQ was in his flat the day he died and will take DNA samples from up to 50 of his colleagues, the Daily Mail reported.

Giving her verdict in the inquest into the 31-year-old's death, Dr Fiona Wilcox said he was probably killed and it "remained a legitimate line of inquiry" that the secret services may have been involved in the death.

But the 21-month investigation has yet to yield a culprit, with forensic experts still hoping for a breakthrough from DNA tests on a green towel discovered in his kitchen.

Mr Williams would have been unlikely to invite a third party who was not a family member into his home, Dr Wilcox observed, adding: "If a third party was present at the time of his death, in my view that third party would have to have been someone he knew or someone who was there without an invitation."

Mr Williams's relatives later attacked failures by secret services and police after the coroner said "many agencies fell short" in their investigation of the death riddle.

Criticising the inquiry, she warned it was unlikely the mystery would "ever be satisfactorily explained".

But she said: "The cause of his death was unnatural and likely to have been criminally mediated.

"I am therefore satisfied that on the balance of probabilities that Gareth was killed unlawfully."

The lack of hand and footprints in the bathroom was "significant", she said, telling the court: "In relation to the prints found within the bathroom, in my view what was more significant was what was not found rather than what was found."

It was "highly unlikely" Mr Williams died alone, and had he been "carrying out some kind of peculiar experiment, he wouldn't care if he left any foot or fingerprints", Westminster Coroner's Court heard.

As the eight-day hearing ended, relatives spoke out for the first time about their grief being "exacerbated" by MI6's "reluctance and failure" to assist the police inquiry.

In a statement read out by their solicitor, they said they were "extremely disappointed" at "total inadequacies" in the probe into the death of their son and brother, who was on secondment to MI6 from GCHQ at the time.

Scotland Yard meanwhile vowed to explore new evidence that has come to light and Sir John Sawers, chief of the Secret Intelligence Service, apologised "unreservedly" for delays in raising the alarm about the death.

Mr Williams, a fitness enthusiast originally from Anglesey, North Wales, was found in the bag in his flat in Pimlico, central London, on August 23 2010.

Pathologists said he would have suffocated within three minutes if he was alive when he got inside the 32-inch by 19-inch holdall.

The coroner agreed that Mr Williams was suffocated by carbon dioxide, possibly as an onset of a short-acting poison.

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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.

Detective Chief Inspector Jackie Sebire, who is leading the investigation, said the inquest had raised "several new lines of inquiry and the investigation will now refocus and actively pursue all the evidence heard and all the new lines of inquiry".