Constable Stephen Carroll, 48, was shot dead in his patrol car
Two men and a woman are still being questioned by police over the murder of Constable Stephen Carroll.
The police officer was shot dead as he answered a distress call in Craigavon, County Armagh, on 9 March last year.
Police arrested a 40-year-old man in Lurgan and a 36-year-old man and 37-year-old woman in Craigavon on Tuesday morning.
A teenager and a 38-year-old man have previously been remanded in custody charged with the murder.
The dissident republican group the Continuity IRA said it killed Constable Carroll, who was 48 and a married man from Banbridge.
He was murdered two days after the Real IRA shot dead two soldiers outside Massereene Barracks in Antrim.