A man has been arrested in relation to the murder of Detective Garda Adrian Donohoe in Co Louth five years ago.
The father-of-two was shot dead outside Lordship Credit Union in Bellurgan in Co Louth on 25 January 2013.
A man in his 20s was arrested at around 7.15pm outside Wheatfield Prison.
He had completed serving a sentence for roadside offences.
He has been taken to Dundalk Garda Station where he an be questioned for up to three days.
Det Donohoe and a colleague, Detective Garda Joseph Ryan, were on a cash escort from a number of credit unions on the Cooley Peninsula when an armed gang blocked them in to a car park outside Lordship Credit Union.
When Det Donohoe got out to investigate, two gunmen ran towards him and one shot him dead.
Det Ryan was then held at gunpoint by two of the raiders while the others robbed cash and other items from the credit union employees.
Earlier this year, gardaí said the suspects for the murder were known to them.