A 59-year-old man was being quizzed by detectives last night in relation to the murder of a former IRA man turned informer 15 years ago.
Eamon Collins (45), was stabbed and beaten on a country road just outside Newry. It is believed Provisional IRA members from south Armagh murdered the father-of-four for turning supergrass.
The suspect was detained in Newry yesterday afternoon and a house searched. He was taken to Antrim police station for questioning.
Mr Collins was knocked down by a vehicle, attacked and knifed while out walking his dogs on January 27, 1999, in the Dorans Hill area near the city.
Last month, detectives said they had made a DNA breakthrough in the hunt for the killers. Former customs officer Collins turned supergrass after being arrested in 1985 but retracted his statements under pressure from his family.
He was subsequently charged with five murders and dozens of terrorist offences but was not convicted and returned to live in Newry.
In 1997, Collins wrote a devastating expose of the IRA, Killing Rage, based on his life as a terrorist.