Published Sunday, 04 November 2012
David Black, who died in an ambush on the M1 (© Pacemaker)
The pair, aged 44 and 31, were detained in the Lurgan area on Friday morning. They were released unconditionally.
A 29-year-old man, who was arrested in Co Leitrim on Friday evening, is still being questioned by Gardaí in connection with the murder.
Mr Black, a 52-year-old father-of-two from Cookstown, was ambushed by gunmen while driving to work at Maghaberry along the M1 near Lurgan on Thursday morning.
A number of shots were fired at his black Audi A4 from a dark blue Toyota Camry with Dublin-registered number plates, which pulled up alongside.
Mr Black is the 30th prison officer to be murdered in Northern Ireland since 1974.
His funeral will take place on Tuesday.
Anyone with information about David Black's murder is asked to contact the special incident room at Lurgan PSNI station on 028 38 315291 or Crimestoppers on 0800 555 111.
© UTV News