Two men questioned over Adrian Donohoe murder
The inquiry has stretched as far as the US in a bid to track suspects.
Two men remain in Garda custody after being detained in connection with the murder of Detective Adrian Donohoe.
The first man, aged in his 20s, was arrested in Dublin on Sunday evening and was taken to Dundalk station where he continues to be questioned.
The second man, arrested separately, is aged in his 60s and was arrested in Dundalk on Monday evening.
He was taken to Balbriggan station in north Dublin.
Both men are being held under the provisions of section 50 of the Criminal Justice Act 2007.
Detective Donohoe was shot dead on January 25 2013 as he escorted cash from the Lordship Credit Union on the Cooley Peninsula in Co Louth to a nightsafe.
The 41-year-old father-of-two was waiting to travel in a three-car convoy with the gardai and credit union staff when it was ambushed by an armed gang.
He was shot and his partner was taken at gunpoint from the car.
The armed gang escaped with 4,000 euro in cash while Detective Donohoe died at the scene.
Last month, on the fifth anniversary of the detective’s death, a direct appeal was made by gardai to the families of his killers to “do the right thing” and come forward with information.