Police investigating the murder of Northern Ireland prison officer David Black have arrested a 46-year-old man.
The man was arrested in Lurgan, County Armagh following the investigation into the shooting which occurred along the M1 motorway near Portadown.
Black, 52, was gunned down as he drove to work at the Maghaberry prison. Crimestoppers had offered a £10,000 reward for anyone who can provide information about his killers.
Three men, two in Northern Ireland and one in the Republic, were previously arrested but have since been released..
The Police Service of Northern Ireland believes dissident Republicans who are protesting against prison conditions at Maghaberry are responsible for the killing.
Black, from Cookstown, is the 30th prison officer to be killed in Northern Ireland since 1974 and the first since 1993.
Thousands of people attended his funeral at his hometown in County Tyrone.
Reverend Tom Greer, minister of Molesworth Street Presbyterian Church, said: "David Black was a man of honour and principle, a man of kindness and generosity, a man committed to peace and prosperity in Northern Ireland - all those things completely the opposite of the murderous thugs and bloodthirsty criminals who took David's life."
The family requested Sinn Fein politicians not attend the service.