The family of Gareth Williams have said they are "naturally disappointed" it is not possible to state with certainty how the codebreaker died.
They said in a statement they back the coroner's verdict that Gareth was probably unlawfully killed over the latest police conclusions.
They said: "We consider that on the basis of the facts at present known the Coroner's verdict accurately reflects the circumstances of Gareth's death."
They added: "We still however remain very disappointed over the failure of his employers at MI6 to take even the most basic enquiries concerning Gareth's welfare when he failed to attend for work on the 16th August, 2010.
"We believe that if proper steps had been taken in the same manner as any reasonable employer would have undertaken further information relating to the cause of his death might have become apparent and not have been lost due to the length of time before Gareth's body was found."
Spy's family disagree with new police conclusion. They back coroner's view prob unlawfully killed. Again criticise MI6 failures after death
Working at MI6 is not like James Bond, one of the security chiefs told MPs that operatives are given far more supervision.
"The idea of sending an agent off into the field like James Bond, then he comes back two months later and reports... that doesn't work that way," Sir John Sawers, chief of MI6, said. "Our people in the field will have constant communication with us."
Sir Malcolm Rifkind has said that security chiefs speaking to MPs in public today was "an historic occasion" that will be repeated.
The Chair of the Intelligence and Security Committee added that he believed those involved were glad of the chance to speak publicly.
He said: "Many of them have been upset at the accusations that they have been doing something improper or doing something unreasonable to their fellow citizens.
"I suspect they were pleased to have the opportunity in public to speak about the work their own staff do and how important it is to the national interest."
Britain's enemies are "rubbing their hands with glee" over whistleblower Edward Snowden's NSA leaks, the MI6 chief said.Read the full story ›
Just out of spy chiefs session. Felt key line the attack on Snowden leaks that Al Qaeda would be lapping up, enemies rubbing hands with glee
Spy chiefs clear they believe Snowden leaks & media coverage of it caused damage to their operations. Terrorists now changing communications
MI6 chief Sir John Sawers said the leaks from NSA whistleblower Edward Snowden "have been damaging and put operations at risk."
Al-Qaeda is "lapping up" the leaks and Britain's enemies are rubbing their hands with glee, the British intelligence chief added.
Asked if GCHQ could guarantee it does not operate beyond UK law, Sir Iain Lobban replied: "I can give you that guarantee. I believe that to be true. We are subject to the law."
Some work that GCHQ carries our is "necessarily secret," Sir Iain Lobban said.
"I don't think secret means unaccountable in any sense."
"I don't think secret means sinister," he added.
"We do not spend our time listening to the telephone calls or reading the emails of the majority," GCHQ boss Sir Iain Lobban told the committee.