Two men arrested in connection with the murder of prison officer David Black have been released.
Mr Black, 52, was shot dead as he drove to work on the M1 in Co Armagh earlier this month.
The suspects, aged 34 and 42, were detained in Coalisland, Co Tyrone, earlier this week.
A dissident republican group calling itself the 'IRA' claimed responsibility for the murder. The two men were the fifth and sixth detained and subsequently released by detectives investigating the shooting.
