Gardaí have arrested a second man in connection with the 2006 murder of former senior republican and self-confessed British agent Denis Donaldson.
The man, who is in his 30s, was arrested yesterday evening in Donegal and is being held under the Offences Against the State Act.
The development follows yesterday's arrest in Donegal of a 70-year-old man.
Both men are being held at Letterkenny Garda station.
Donaldson's murder took place at a remote farmhouse at Cloghercor, Doochary, near Glenties, Co Donegal, in April 2006.
There was initial suspicion that Donaldson may have been killed by members of the Provisional IRA because he had worked as an informant for British intelligence for two decades. But three years after the killing the Real IRA said it had murdered him.
Senior security sources said last night that gardaí now accept the Real IRA admission is valid.
The revelation that Donaldson was working as a British agent caused shock within republicanism, especially as he was such a senior and veteran republican figure and close to Sinn Féin president Gerry Adams.
He was Sinn Féin administrator at Stormont and had the ear of Mr Adams and other senior party members. Mr Donaldson was also a close friend of Bobby Sands, who died on hunger strike and served time with him in the Maze prison.
As Stormont party administrator he and two other men were arrested in October 2002 for being allegedly involved in an IRA spy ring at Stormont. The affair collapsed the Northern Executive and Assembly the same month.
In December three years later the North’s Public Prosecution Service dropped the spying charges saying that it would not be in the “public interest” to proceed.
Later Mr Adams revealed that Donaldson worked for British intelligence. Shortly afterwards Donaldson said he had been recruited in the 1980s after “compromising myself during a vulnerable time in my life”.