Published Friday, 23 November 2012
David Black died in an ambush on the M1 on Thursday morning. (© PA)
The pair, aged 34 and 42, were detained earlier this week in Coalisland, Co Tyrone, by detectives from the Serious Crime branch.
They were taken to Antrim for questioning but were later released.
Mr Black, a prison officer from Cookstown, was ambushed by gunmen as he travelled to work at Maghaberry Prison earlier this month.
A dark blue Toyota Camry with Dublin registered number plates pulled up alongside the 52-year-old's black Audi A4 on the M1.
Shots were fired and Mr Black's car immediately veered off the road and into a deep drainage ditch. He was the 30th prison officer to be murdered in Northern Ireland since 1974.