Martin O'Hagan was shot dead while walking home with his wife
A 28-year-old man is being questioned about the murder of Sunday World journalist Martin O'Hagan in Lurgan seven years ago.
He is being held at Antrim police station by detectives from the retrospective murder review unit.
A 40-year-old man arrested last week remains in custody.
Two men have been charged with murdering the 51-year-old, who was shot dead as he walked home from a pub with his wife in September 2001.
At the time, the murder was claimed by the Red Hand Defenders, a cover name used by both the Loyalist Volunteer Force and the Ulster Defence Association.
Mr O'Hagan had built a reputation for stories about paramilitaries and drug-dealing.