A 46-year-old Lurgan man has been arrested by detectives investigating the murder of prison officer David Black.
The man has been taken to Antrim Serious Crime Suite for questioning.
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.
Two men, 44-year-old Colin Duffy and a 31-year-old man, detained in the Lurgan area on Friday in connection with the murder were released unconditionally on Sunday.
A 29-year-old man arrested in Co Leitrim on Friday in relation to the murder has also been released without charge.
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.