Two men and a woman have been arrested over the murder of Northern Ireland prison officer David Black.
Mr Black, 52, was shot as he drove to work on a motorway in Co Armagh on November 1. Dissident republicans claimed responsibility.
The father-of-two worked at the high security Maghaberry jail in Co Antrim.
Police said a man aged 36 was arrested on Tuesdayin Co Tyrone and taken to Antrim police station for questioning.
Mr Black was the first prison officer murdered in Northern Ireland for 20 years.