Forensic scientists cannot establish if a British spy was poisoned before being padlocked in a bag because it took his employers MI6 a week to realise he was missing, an inquest has heard.
Forensic expert Denise Stanworth told the hearing in London that "we cannot rule out volatile agents" in the death of Gareth Williams two years ago as she was asked how reliable toxicology tests can be nine days after death.
The decomposition of the body made it impossible to establish exactly which substances were present in the codebreaker's body, she said.
Williams' boss at MI6, Britain's external intelligence agency, earlier apologised to the 31-year-old's family for failing to raise the alarm about his disappearance and conceded the error may have hampered police inquiries.
Speaking Thursday from behind a screen, the woman -- identified only as Witness F -- offered a full apology for MI6's slow response to Williams's disappearance in August 2010.
"We are profoundly sorry about what happened, she said.
"It shouldn't have happened and we recognise that the delay in finding Gareth's body has made it even harder for the family to come to terms with his dreadful death and we are truly sorry for that.
"I also appreciate the delay had some impact on the police investigation."
Williams' relatives left the hearing in tears after it was revealed MI6 had failed to realise he was missing.
When police finally entered Williams' flat in Pimlico, central London, they found his naked body padlocked in a red holdall placed in his bath.
Police have been unable to establish a cause of death, though they have unearthed no proof that anyone was with him when he died.
His family have said they believe secret agents versed in the "dark arts" tried to cover up his death.
But the five-day inquest, due to end on Friday, is looking into whether he could have entered the bag alone, after speculation he might have done so as part of a sex game.
Examination of his home computer showed he had also visited websites about claustrophilia -- the love of enclosure -- and bondage and sadomasochism, the inquest has heard.
High-end women's clothing and shoes worth some £20,000 ($32,400, 24,500 euros) were found in the immaculate flat.
Source: AFP European Edition