Update 3.30: One of two men arrested in connection with the murder of Denis Donaldson in Co. Donegal, has been released without charge.
Donaldson, who was exposed as a British spy, was killed near Glenties in April 2006.
Two men aged in their 30 and 40s were arrested last night.
The suspect in his 40s was released without charge today, the man in his 30s is continuing to be questioned at Letterkenny garda station.
Gardai say the investigation is ongoing.
Earlier: Two men have been arrested in Donegal in connection with the murder of former Sinn Féin official and British agent Denis Donaldson over a decade ago.
Denis Donaldson, a senior Sinn Féin official and close colleague of Gerry Adams, was shot dead at a remote cottage near Glenties, Co Donegal, in 2006 after being exposed as a British spy.
He had been living at the cottage since his exposure as an MI5 agent the previous year.
Gardaí arrested two men, one aged in his 30s and the other in his 40s, on Sunday.
They were being questioned in Letterkenny Garda Station and they can he detained for 72 hours.
The Real IRA claimed responsibility for the murder three years later but the circumstances surrounding Mr Donaldson’s outing and subsequent assassination have been shrouded in mystery.
The sequence of events surrounding Mr Donaldson's death dated back to 2002 after three men including Mr Donaldson were arrested following a raid on Sinn Féin’s Stormont office. The power-sharing executive between unionists and nationalists collapsed and Government restored direct rule to Northern Ireland a week later.
In 2005 charges against three men were dropped and within days Sinn Féin said Mr Donaldson was a British agent and expelled him from the party. He later said he had worked as a spy since the 1980s.
More to follow.