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. However 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, originally from Anglesey, North Wales, 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 told Westminster Coroner's Court: "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."
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.
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".