A man has been arrested in connection with an IRA bomb attack that killed a Catholic nun and three police officers in Co Armagh in 1990.
The 54-year-old suspect was detained at Belfast International Airport this morning.
He is the second man detained in relation to the attack in less than a week.
A 55-year-old man arrested and questioned last Thursday was released pending a police file being submitted to Northern Ireland's Public Prosecution Service.
Sister Catherine Dunne, Constable William Hanson, Reserve Constable Joshua Willis and Reserve Constable David Sterritt were killed when a landmine exploded on the Killylea Road, Armagh, on 24 July 1990.
Another woman was seriously injured in the blast.
The arrests have been carried out by the Police Service of Northern Ireland's legacy investigation branch.
The suspect detained this morning has been taken to the PSNI's serious crime suite at Musgrave station in Belfast.