Gareth Williams, the MI6 worker found naked and dead inside a padlocked bag in the bath at his London apartment in 2010, probably did it to himself, Scotland Yard has found.

The finding counters speculation that Williams was the victim of a hit by the security services, which Westminster Coroner Fiona Wilcox said earlier this year remained a "legitimate line of inquiry."

The Telegraph reportedthat a review of the case by Scotland Yard's murder squad — which re-interviewed Williams' colleagues from MI6 and taken DNA samples over the last seven months — concluded that he probably died alone.

"They have been unable to find any trace of anyone who should not have been in the flat and every reason to believe that Gareth may have climbed into the bag himself and been unable to get out," a source close to the inquiry said.

Williams, 31, a cryptology expert according to Fairfax New Zealand, had worked for Britain's eavesdropping service GCHQ (Government Communications Headquarters) but was temporarily attached to MI6, the UK's spy agency, when he was found dead just a few days after returning from a trip to the US.

Described as an introverted math genius, he had an unorthodox sexual history, according to evidence given at the coroner's hearing.

His landlord testified that she once found him handcuffed to his bed, embarrassed and asking for help.

Meantime, forensic experts reportedly found about $32,000 worth of luxury women's clothing, shoes and wigs in his apartment.

Williams was also found to have been visiting bondage and sadomasochism websites, including several related to claustrophilia - a desire for confinement in enclosed spaces.

He was discovered in the fetal position inside the red holdall, with two keys to the padlock also inside the bag.

However, after hearing from two specialists who unsuccessfully attempted to lock themselves in an identical bag, 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.

Wilcox said was unlikely that the death would ever be "satisfactorily explained." The verdict was highly critical of the Metropolitan police's counter-terrorism branch and MI6, The Guardian reported.