A senior British detective said Tuesday that specks of another person's DNA were found on the zipper and lock of a sports bag that contained the body of a U.K. codebreaker, casting doubt on theories the young spy climbed into the bag himself as part of a sex game.

Gareth Williams worked for Britain's secret eavesdropping service GCHQ and was attached to the country's MI6 overseas spy agency when he was found in the bathtub of his central London home in August 2010.

The discovery of the 31-year-old's body launched a media frenzy and a flurry of conspiracy theories — there were no signs of struggle, and no drugs or poison in Williams' body.

While detectives have suggested Williams may have died in a sex game gone wrong, his family has claimed that British spy agencies may have been involved in the death.

An inquest into his death is investigating whether Williams could possibly have climbed inside the sports bag and locked it from the inside. But the new DNA evidence has deepened the mystery of how he died.

Detective Chief Inspector Jackie Sebire told the inquest that "two minor components" of DNA that did not match Williams' were found on the zip and padlock of the North Face sports bag containing his body.

"My thought, or my opinion, since I went into the scene is that a third party had been involved in the death or by putting the body in the bag," she said.

Sebire noted that she would have expected to find Williams' fingerprints on the floor tiles of the bathroom where the bag was found and also that the spy had not damaged the bag or injured his hands.

Williams' body was found in the fetal position inside the bulging bag.

"He was very muscular, he trained regularly," she said. "It is only my opinion, but I would at least expect some tearing to the netting."

Sebire said there's "limited scope" for disovering more forensic evidence. She also acknowledged the investigation had suffered a setback after detectives spent 18 months investigating a DNA sample found on Williams' hand that had actually come from a forensic scientist involved in the case.

In Britain, inquests must be held when someone dies unexpectedly, violently or from unknown causes.