Two men arrested over the murder of a prison officer in Northern Ireland have been released unconditionally.
Father-of-two David Black, 52, was shot dead as he drove to work on the M1 motorway in Co Armagh earlier this month.
The suspects, aged 34 and 42, were detained in Coalisland, Co Tyrone, earlier this week.
Mr Black, from Cookstown, Co Tyrone, was gunned down in a high-speed motorway ambush as he drove to start his shift at Maghaberry Prison in Co Antrim.
The long-serving officer was nearing retirement.
A dissident republican group styling itself the "IRA" claimed responsibility for the murder.
The two arrested men were the fifth and sixth detained and subsequently released by detectives investigating the shooting.