Slain agent 'accidentally exposed Stormontgate subterfuge'
Denis Donaldson inadvertently "let the cat out of the bag" about republican intelligence gathering at Stormont to another British spy.
The Stormontgate scandal of 2002 saw scores of PSNI officers raid Sinn Fein's Assembly offices after accusations that an IRA spy ring was gathering intelligence at the heart of government.
Donaldson - Sinn Fein's Assembly administrator at the time - was arrested shortly afterwards. Two weeks later, Stormont was suspended.
In last night's Spotlight investigation, a former IRA man and British agent - identified only as Martin - said that he discovered the spy ring after Donaldson told him he was removing sensitive documents from the NIO office at Stormont.
"The common belief is that Denis Donaldson told Special Branch about the spy ring at Stormont - but it was me," the agent said.
The case against Donaldson was dropped in 2005 in order to protect his identity as a British agent. That year he was visited by police who warned him that the media had learned about his role as an agent.
Before long his former staunch supporter, Sinn Fein leader Gerry Adams, held a press conference to reveal his 'scoop' that Donaldson was a spy.
Donaldson admitted the truth himself shortly afterwards.
Martin told Spotlight that Donaldson had "signed his own death warrant".
He went into hiding in Donegal, but in 2006 his isolated cottage was identified by the Sunday World journalist Hugh Jordan.
Two weeks later, Donaldson was dead.
The Stormont raid followed a break-in at Castlereagh police station on St Patrick's Day in 2002, when three men stole sensitive documents used by Special Branch.
Police said they believed a chef from New York, Larry Zaitschek - who was working in the station's canteen at the time - was the IRA's inside man. Donaldson had been working as a British agent since the 1980s, but he failed to tell his handlers about a previous connection he had to Larry the chef.
As an IRA man, Donaldson had travelled the world working as a recruiter and building contacts with groups such as Noraid, the US organisation that provided financial backing to the IRA.
In New York he met and befriended Larry and encouraged him to move to Northern Ireland.
The link later made his spymasters question his true loyalty.
The case against Zaitschek was dropped in 2009, and he has denied any involvement in the break-in.