Gardai are continuing to question a prominent dissident republican over the murder of IRA informer Denis Donaldson.
Gary Donnelly, a member of the 32 County Sovereignty Movement and aged in his 40s, is from Derry but was arrested in Co Monaghan.
Mr Donaldson was shot dead at a remote cottage in Donegal in April 2006.
Just months earlier the former Sinn Fein official publicly admitted being a British agent inside the republican movement for more than 20 years.
Gardai arrested Donnelly in Clontibret, Co Monaghan, on Saturday evening.
This is the third arrest in relation to the investigation.
The prominent dissident republican is being questioned at Monaghan Garda Station where he can be held for up to three days under Section 30 of the Offences against the State Act, 1939.