The 2010 death of Gareth Williams, a British foreign intelligence spy, may never be solved, a coroner said on Wednesday.
Coroner Fiona Wilcox said that it is unlikely that the death of the 31-year-old secret service agent "will ever be satisfactorily explained."
The coroner added that on the "balance of probability," Williams was "killed unlawfully" but due to the insufficient evidence a final verdict of unlawful killing was not ruled.
The mysterious death of the MI6 codebreaker shocked the United Kingdom and investigators have been looking into the case for years, but have found little evidence to reach a conclusion as to how Williams died.
Williams, who worked for Britain's foreign intelligence service, was found dead in the bathtub of his London apartment, which was a safe house for security agents. Williams' naked body was found wrapped in a large red North Face carrying bag but his apartment showed no signs of break-in and no signs of force appeared to have been used against him.
The North Face bag had been padlocked from the outside and pathologists believe that the spy may have been poisoned or suffocated to death.
Williams was reported missing by his Mi6 employers one week after he had died and family members of the late secret service agent believe that evidence in the case may have been tampered with as part of a cover-up.
Detective Chief Inspector Jackie Sebire, who has headed the investigation, also believes that the death was not accidental and that another person was involved in the case.
"My strongest belief is that a third party was involved and I would ask people to search their consciences and come to us to find some resolutions to this case and some peace for his family," Sebire told AFP.