Two men are now being questioned in connection with the murder of Detective Garda Adrian Donohoe in County Louth.
Detective Garda Donohoe was shot dead on the 25th January 2013.
The father of two died during an armed robbery at the Lordship Credit Union in Belurgan.
Last night, a man in his 60s was arrested in Dundalk in connection with the investigation.
He is being held under section 50 of the Criminal Justice Act at Balbriggan Garda station.
On Sunday, a man in his twenties was arrested outside Wheatfield Prison, in relation to the investigation.
He was taken to Dundalk Garda Station, where he can be questioned for up to three days, however gardaí could make a court application seeking to extend his detention.
Gardaí have been working with several international police organisations, including the FBI and PSNI, as part of the investigation into Detective Donohoe's death.