However, police couldn't find Williams' DNA on the lock, palm prints on the rim of the bath, or footprints in the bathroom itself. The coroner, Fiona Wilcox, said that pointed to another person having taken the bag into the bathroom, noting that if Williams had been "carrying out some kind of peculiar experiment, he wouldn't care if he left any foot or fingerprints."
She was also critical in her inquest verdict of MI6, which failed to pass evidence to investigating police, and said that while it seemed unlikely that British intelligence agencies were involved in Williams' death, it was a "legitimate line of inquiry."
Hewitt said there was no evidence that the apartment had been cleaned to remove forensic traces and nothing to suggest a struggle or a break-in.
And he dismissed the idea that Britain's secretive intelligence services had carried out a cover-up, noting that a total of 27 members of staff from both MI6 and GCHQ had been interviewed and that police were given full access to Williams' vetting and personnel file.
"I do not believe that I have had the wool pulled over my eyes," Hewitt said. "I believe that what we are dealing with is a tragic unexplained death."
He added that there was "no evidence to support the theory that Gareth's death was in any way related to his work."
Williams' relatives said in a statement that they were disappointed that the facts remain unclear, but still believed it was likely he had been the victim of foul play.
"We consider that on the basis of the facts known at present the coroner's verdict accurately reflects the circumstances of Gareth's death," the statement said.