LONDON - Post mortem examinations of the British spy found mysteriously dead in his bathtub two years ago have failed to determine how he died. Three pathologists have told the official inquest into his death that asphyxiation or poisoning were the most likely possible causes, but the decomposition of his body prevented them from reaching any firm conclusions.

The naked body of Gareth Williams was found curled up inside a zipped and locked duffle bag in the empty bathtub of his London apartment in 2010. Scotland Yard has been unable to solve the case after a nearly two-year investigation. At the time of his death Williams was working in London as a code breaker for Britain's Secret Intelligence Service (SIS), also known as MI6.

Tests are still being carried out on DNA fragments found by forensic scientists in the apartment, and which are believed to be from at least two other unknown people.

Pathologist Dr. Benjamin Swift has told the court that the post mortem was hampered by decomposition of the body, made worse by heating from radiators inside the apartment, which inexplicably were switched on in the middle of summer. It also took a week for detectives to discover the body after the code breaker failed to show up to work at the headquarters of Britain's intelligence service on August 16. MI6 has blamed a "breakdown in communication" for the delay in raising the alarm, which may have resulted in the loss of crucial forensic evidence.

Although no trace of poison was found in the body of Gareth Williams,  Swift said it could have disappeared from his system in the ten days it took for his corpse to be discovered and then examined.

Another pathologist who gave evidence at the inquest today said he believed Williams was probably alive when he entered the sports bag, which was fastened with an outside padlock. No signs of struggle were detected on the body of the intelligence officer. The court was told by two experts last week that it was highly unlikely that the spy would have been able to lock himself into the bag.

Williams was working in London after being seconded to the British spy agency by GCHQ, Britain's secret electronic surveillance agency, where he had previously been employed. His former boss at GCHQ has told the inquest that he was a "world class intelligence officer." "He was considered something of a prodigy," Stephen Gale told the court.

His manager at MI6 has called him "a fully deployable, highly talented officer" who had passed exams to do some of MI6's toughest covert work six months before he was found dead in August 2010.

Police are still treating his death as suspicious and unexplained. The inquest has been told by police that there was no indication of a break-in at the apartment, and nothing to suggest evidence at the scene was destroyed. Giving evidence today, a third pathologist has described the spy as "a healthy person with no damage, as far as we know no drugs, no trauma, no natural disease."

Police say thousands of dollars worth of women's designer clothes were discovered at his apartment, as well as wigs and make-up. Two friends of the dead man have testified that, to their knowledge, Williams was not gay and had no interest in cross-dressing. The inquest has heard that a police examination of the spy's computer and phone has shown that he made occasional visits to bondage websites and websites about claustrophilia or the love of enclosure. No classified information was found at his apartment.

A fellow spy has told the hearing that an internal review had concluded that Williams' death was not connected to his work, which had included operational assignments with MI6. His family say they believe another person must have been involved in his death. The coroner says she hopes to give her verdict on Wednesday