• Gareth Williams was probably unlawfully killed - coroner • 'Criminally mediated' - third party locked bag and placed in bath • Spy probably died of poison or carbon dioxide inside bag • Clothes did not fit codebreaker and probably bought as gifts • Little evidence death due to bondage games • Family calls on Met chief to review the case and SO15 'failings' • MI6 chief Sawers apologises for delay in raising alarm • Police appeal for information from public as probe goes on
Gareth Williams's death most likely involved a third party and he was either poisoned or suffocated, Dr Fiona Wilcox said.
She said the possibility that a member of the intelligence services was involved in the maths prodigy's death remained a "legitimate line of inquiry" for police.
The head of MI6, Sir John Sawers, apologised to Mr Williams's family for failing to report him missing for a week.
In a statement, family members said the delay had "exacerbated" their grief. They also criticised the intelligence service for its "failure and reluctance" to make information available.
The Metropolitan Police announced an urgent review of the case after concerns were raised over how some evidence was handled by MI6 and counter-terrorism officers during the two-year investigation.
Martin Hewitt, a deputy assistant commissioner at the Met, said the force was still investigating weak traces of DNA of at least two other people found in the flat in an attempt to identify a suspect.
Tests on whether there is a DNA sample on a towel found in Mr Williams's kitchen could also be concluded within weeks.
There is also an investigation into whether a telephone that had been reset shortly before Mr Williams died could have held any clues. The coroner wondered whether it may have contained evidence of an arrangement to meet someone.
The naked, decomposing body of Mr Williams, a codebreaker on secondment to MI6 from GCHQ, the signals intelligence agency, was found in a padlocked holdall in the bath of his flat in Pimlico, London, in August 2010.
Despite an intensive police investigation, no one has been arrested and the circumstances surrounding his death have remained a mystery.
At the end of an eight-day inquest, Dr Wilcox concluded that a third party was most likely involved, adding: "The cause of death was unnatural and likely to have been criminally mediated. I am therefore satisfied on the balance of probabilities that Gareth was killed unlawfully."
Recording a narrative verdict at Westminster coroner's court, she said that Mr Williams was probably alive when he entered the bag and died either from an "unknown poison" or was overcome by carbon dioxide in the tight space.
She criticised the way MI6 and Det Supt Michael Broster, of the Met's counter-terrorism unit, had handled aspects of the case.
Det Supt Broster acted as a link between the intelligence service and the Met team investigating the death, headed by Det Chief Insp Jackie Sebire.
It emerged this week that nine memory sticks potentially belonging to Mr Williams and a sports bag similar to the one in which he was found were discovered at MI6 but never disclosed to DCI Sebire.
There were also concerns over what precautions were taken to ensure his belongings were secured at work following his death.
An MI6 spokesman added: "We fully cooperated with the police and will continue to do so during the ongoing investigation. We gave all the evidence to the police when they wanted it; at no time did we withhold any evidence."