A 66-year-old man is due in court in Dublin later in relation to the murder of two soldiers in the North in 1972.
His arrest by gardaí in Donegal follows a joint operation with the PSNI.
The arrest was made yesterday in County Donegal under a European Arrest Warrant.
The man they detained is wanted in the North, on suspicion of the murder of two Ulster Defence Regiment soldiers, and on suspicion of aiding and abetting an explosion.
Lance Corporal Alfred Johnston and Private James Eames died when a device exploded in a car they were checking on the Irvinestown Road in Enniskillen in 1972.
The process of extraditing the 66-year-old is set to begin later, when he appears before a court in Dublin.
The PSNI says it has been liaising closely with Gardaí on the case, and it says the arrest demonstrates the benefits of such joint operations.