Background: Donaldson sparked speculation over 'Stormont spy ring'
Denis Donaldson's role as both IRA man and British agent before his death in 2006 sparked speculation over an alleged Republican spy ring at Stormont.
The 'Stormont Gate' scandal in 2002 saw scores of PSNI officers raid Sinn Féin's offices there, after accusations that an IRA spy ring was intelligence- gathering.
Denis Donaldson - Sinn Fein's Assembly Group administrator at the time - was arrested shortly afterwards. Two weeks later the Stormont Assembly was suspended.
The Stormont raid followed a break-in at Castlereagh Police Station on St Patrick's Day in 2002, where 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.
Zaitschek always protested his innocence and the case ultimately collapsed after police revealed they could not disclose new evidence uncovered over the raid.
Donaldson had been working as a British agent since the 1980s, but he declined to tell his handlers about a previous connection to 'Larry the chef'. As an IRA man he had travelled the world working as a recruiter and building contacts with groups such as the Northern aid group, NORAID.
In New York, he met and befriended Larry and encouraged him to move to Northern Ireland. The connection made his spymasters question his true loyalty.
A 'Spotlight' investigation claims that Donaldson also knew about the spy ring at Stormont.
The man identified only as Martin - said he discovered the spy ring after Donaldson "let the cat out of the bag" to him.
"The common belief is Denis Donaldson told Special branch about the spy ring at Stormont, but it was me," he said. The case against Donaldson was dropped in 2005, something 'Spotlight' say they understood was done to protect his identity as a British agent. Before long, his former staunch supporter Gerry Adams held a press conference with the "scoop" that Donaldson was a spy.
Donaldson admitted the truth shortly afterwards. Martin told 'Spotlight' he had "signed his own death warrant".
A Garda investigation into his murder is ongoing.
In July, a 74 year-old man was charged over withholding information in connection with the murder.
'Spotlight' said they understood the investigation is now focused on a separate individual outside the Irish Republic described as "sympathetic to dissident republicans".
A journal written by Denis Donaldson is currently being held by Garda investigators.
He was encouraged to write it by republicans as part of his debriefing process.