A man arrested in connection with the murder of prison officer David Black in Northern Ireland has been released unconditionally.
The 46-year-old from Lurgan, Co Armagh, was the fourth man detained and then released by detectives investigating the shooting.
Mr Black, a 52-year-old father of two from Cookstown, Co Tyrone, was gunned down in a high-speed motorway ambush as he drove to work at Maghaberry prison in Co Antrim last week.
The long-serving officer was nearing retirement.
Dissident republicans have been blamed for the attack.
The Crimestoppers charity has offered a £10,000 reward for information that leads to the conviction of Mr Black's killers.
At his funeral earlier this week his daughter Kyra described the prison officer as her special hero.
PA