Tests on the body of MI6 spy Gareth Williams have revealed no traces of any foreign substances that may have led to his death.
No evidence of drugs, alcohol or poisons were found during a battery of tests conducted by toxicologists, sources close to the inquiry said.
The 30-year-old GCHQ code-breaker's naked and decomposing body was found in a padlocked holdall in the bath of his Pimlico flat on August 23.
The mysterious circumstances of Mr Williams' death sparked an international frenzy of speculation earlier this year.
Coroner Dr Paul Knapman is due to review the case in private next Wednesday after opening an inquest on September 1.
A Metropolitan Police spokesman said: "Results from comprehensive further toxicology tests carried out in relation to the death of Gareth Williams have come back negative, showing no trace of any drugs, alcohol, poisons or any other substances that would indicate cause of death.
"There are no plans to carry out any further tests of this type, but enquiries continue to try and establish a formal cause of death.
"Mr Williams' death remains suspicious and unexplained and enquiries into the circumstances continue."
Scotland Yard detectives, led by Detective Chief Inspector Jackie Sebire, continue to try and identify what led to Mr Williams' death.
They have been hunting for a man and a woman seen calling at the communal door of his Alderney Street home.
Witnesses said the Mediterranean couple, aged in their twenties, were let into the property late on an evening in June or July.
The spokesman said: "The police are still keen for the couple to come forward, or receive any information regarding them from members of the public."
Mr Williams' body was found by officers who called at his flat after colleagues raised the alarm that he had not been seen for some time.
There was no sign of any forced entry to the property or a disturbance inside and nothing is believed to be missing.
He was found unclothed, in a zipped and padlocked red North Face holdall in an empty bath in the ensuite bathroom.
A first post mortem examination could not identify a cause of death and police sent off numerous intimate samples for further tests.
Mr Williams, of Anglesey, North Wales, was last seen alive on August 15, eight days before he was found dead in the £400,000 property.
Police have released CCTV footage of him entering Holland Park Underground station at about 3pm the previous day.
The cycling fanatic was on a one year secondment to MI6, based in nearby Vauxhall Cross, from his work at the GCHQ listening post in Cheltenham.
His family have lashed out at rumours the mathematics prodigy was involved in risky sexual practices, saying they had been "very distressing".
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