MI6 and a senior detective were accused today of failing to disclose vital evidence in the death riddle of spy Gareth Williams.
A coroner suggested the counter-terror officer was not being "completely impartial" towards secret services during the Scotland Yard inquiry.
Detective Superintendent Michael Broster was criticised after his assistant was told he had offered evidence as "helpful as a London pea souper" at the inquest into Mr Williams's death.
Coroner Fiona Wilcox and the family's lawyer both delivered angry outbursts after it emerged that nine computer memory sticks and a black bag were overlooked for 21 months after the death.
The lead detective on the case was told about the evidence only yesterday.
Dr Wilcox told Mr Broster, who was unable to rule out secret service involvement in the death, that he was offering "total non-sequitur" reasons for failing to pass on evidence.
"I suggest that this means you have not been completely impartial in this case," she told him at Westminster Coroner's Court.
As Dr Wilcox ordered police to bring the missed evidence into the inquest into Mr Williams's death, family barrister Anthony O'Toole told police they had not taken the incident seriously enough.
The lawyer said: "If this had not involved SIS (Secret Intelligence Service) and it was the Kray twins you were investigating, you would have gone into this in far more detail."
The North Face bag - similar to the one in which Mr Williams was found dead at his flat - was discovered by officers under the spy's desk at MI6's London HQ.
MI6 also examined computer equipment belonging to Mr Williams without telling police, the inquest heard.
Members of Mr Williams's family shook their heads as Detective Constable Colin Hall, of the force's counter-terror SO15 branch, said his search of the agent's Vauxhall HQ was called off shortly after the spy was found dead.
Mr Hall said "there was stuff in there of a sensitive nature" in the bag but, when asked what, he said he could not remember.
Mr O'Toole added: "That's about as helpful as a London pea souper."
Detective Chief Inspector Jackie Sebire, the lead officer on the case, said she had no knowledge of the existence of memory sticks in his cabinet at work or the bag.
She said: "I would have expected to have been told.
"What I knew was that Gareth's email accounts had been checked but I did not know that other media had been checked."
Mr Hall was ordered to re-examine the black bag in the courtroom as the inquest heard its last day's evidence.
The 31-year-old fitness enthusiast was found naked, curled up in a padlocked holdall in the bath of his flat in Pimlico, central London, on August 23 2010.
Dr Wilcox asked Mr Hall: "Would you not consider that seizing another sports bag might be relevant?"
He replied: "I was told there was nothing there about Gareth's death."
He later said: "I will do what I'm told."
He added that "we had not completed our search" when he was told to wrap up efforts on his first visit on August 26.
Pathologists said yesterday that Mr Williams would have suffocated within three minutes after getting inside the bag.
Poisoning and asphyxiation are the "foremost contenders" in solving the death riddle, they added.
Mr Broster said later that he was "completely impartial" and secret services had been helpful with inquiries.
"I have seen no information or evidence that someone is involved. I am not saying that a member of SIS is not involved. I don't know."
Ms Sebire said she remained convinced Mr Williams' death was "suspicious".
"Obviously a lot of information has come out through the course of this inquest which we have not been party to," she told the inquest.
Detective Chief Superintendent Hamish Campbell is set to consider whether there are any new lines of inquiry in the next few weeks.
Ms Sebire added: "Once the inquest is over, Mr Campbell will review the structure and we will look at all lines of inquiry."
She added: "It's an ongoing process as it has been since it started."
There will be inquiries into computer equipment and "Gareth's work colleagues", Ms Sebire said.
She said Mr Williams was a "brilliant young man who spent his entire life working for his country and was commended for it".
She added: My strongest belief is that a third party was involved and I would ask people to search their consciounces and come to us to find some resolutions to this case and some peace for his family."
The inquest was adjourned until tomorrow when the coroner will hear final legal submissions before delivering her verdict.