Three police officers died in the blast
A man has been arrested in connection with a 1990 bomb attack in Armagh that killed four people.
The 55-year-old has been detained by detectives from PSNI Legacy Investigation Branch.
He was arrested on Thursday morning on suspicion of a number of offences.
These included the murder of three police officers and a Catholic nun.
They died in the explosion on the Killylea Road in Armagh on July 24th, 1990.
Constable William Hanson, Reserve Constable Joshua Willis, Reserve Constable David Sterrit and Sister Catherine Dunne were killed when a landmine was detonated.
Another woman was also seriously injured in the blast.
The arrested man has been taken to a Belfast police station for questioning.