LONDON (AP) — A coroner acknowledged today that the puzzling death of a British spy whose naked body was found inside a locked sports bag may never be solved.

Coroner Fiona Wilcox said it was unlikely that the demise of Gareth Williams, 31, would “ever be satisfactorily explained,” despite a 21- month police inquiry, and her own weeklong series of inquest hearings.

Williams worked for Britain’s secret eavesdropping service GCHQ but was attached to the MI6 overseas spy agency when his badly decomposed remains were found in August 2010 at his London apartment, in the padlocked bag and inside a bathtub.

Wilcox said “most of the fundamental questions in relation to how Gareth died remain unanswered,” despite the efforts of detectives, Britain’s intelligence agencies and the spy’s family. She told Williams’ relatives, who were at Westminster Coroner’s Court to hear the verdict, that evidence presented during the inquest hearing wasn’t sufficient to support a verdict of unlawful killing which they had sought.

However, Wilcox said that while it appeared unlikely, it continued to be a “legitimate line of inquiry” that British intelligence agencies may have been involved.

Family lawyer Anthony O’Toole has previously said Williams’ relatives insist his secret work must be connected to his death. They suspect “the dark arts of the secret services” may be behind a coverup, O’Toole said.

Wilcox delivered a so-called “narrative verdict”

— a lengthy but inconclusive ruling which is available when there isn’t clear evidence of natural causes, suicide or unlawful killing.

In Britain, a coroner’s task is to outline the circumstances of how and when a person died — rather than apportion blame, or recommend criminal charges.

Police confirmed today that an investigation into the spy’s death remains active.

Officers are uncertain exactly how Williams died and have so far made no arrests, although a senior detective told the inquest that she believes at least one other person must have been involved.

Experts told the hearing that it appeared almost impossible that Williams could have climbed inside the sports bag and then locked it himself.

Police have indicated Williams’ death may have had links to his private life and an apparent interest in sadomasochism — possibly during a sexual encounter gone awry. The hearing was told Williams previously had to call for help after he tied himself to his bed and couldn’t escape.

His relatives, however, insist his demise must be related to his work and suspect foul play.

Pathologists told the hearing that poisoning or asphyxiation may have killed Williams, but acknowledged they can’t be certain of the exact cause because his cadaver badly decomposed as it lay undiscovered for several days.