A coroner's damning verdict on the death of MI6 code-breaker Gareth Williams shows the need for more open system, campaigners said today.
Mr Williams's body was found naked, curled up in a padlocked holdall in the bath of his Pimlico flat on August 23 2010.
Sitting at Westminster Coroner's Court, Dr Fiona Wilcox condemned both MI6, which failed to report him missing for a week, and the Metropolitan Police's counter-terrorism unit SO15 for not passing potentially key evidence to detectives.
Nine computer memory sticks and a mysterious black bag were overlooked in the inquiry until lead detective Jackie Sebire was told about them earlier this week.
Despite a 21-month police inquiry and a seven-day inquest "most of the fundamental questions in relation to how Gareth died remain unanswered," Dr Wilcox said.
She recorded an open verdict but said it was "unlikely" the circumstances surrounding the death "will ever be satisfactorily explained" and suggested "on the balance of probabilities" Mr Williams had been unlawfully killed.
Campaigners say the verdict highlights problems being created by the government's justice and security green paper, which proposes that certain inquests be heard in secret - meaning cases such as this might never be heard in public.
Campaign group Inquest co-director Deborah Coles said: "This case demonstrates once again how crucial the inquest process is in holding the state to account and how vital it is that this process is open and transparent.
"All the more reason why the proposals for inquests to be held behind closed doors should never be implemented."