Garda Commissioner has appealed for information, saying Adrian Donohoe represented "all that is good about An Garda Síochána"
The Garda Commissioner says the force is as determined as ever to bring Detective Garda Adrian Donohoe's killers to justice.
On January 25th 2013, Detective Donohoe was killed in the line of duty outside the Lordship Credit Union in Louth while trying to stop an armed robbery.
Marking the fourth anniversary of his death, Commissioner Noirin O'Sullivan says he was the epitome of "all that is good about An Garda Síochána".
She said: "In his professional and personal life he was dedicated to the community he served. Whether it was his work in Dundalk Garda Station or giving his time to coach underage teams at St Patrick’s GAA in Lordship, Adrian was always focused on helping and supporting others."
Officers have followed thousands of leads in the investigation but nobody has ever been prosecuted.
The latest appeal for information claims there are still people out there who know who the killers are, and stresses that it is "never too late to do the right thing".
"We cannot do this alone, we still need the public’s help," Commissioner O'Sullivan adds. "Even the smallest piece of information could be vital."
Anyone with information on the murder of Adrian Donohoe can contact the incident room in Dundalk Garda Station on 042-938-8470 or the Garda Confidential Number on 1800-666-111.