Garda Commissioner Drew Harris has said there is no signs at this moment that the shooting of Garda Colm Horkan is part of wider organised crime.
Speaking to media in Castlerea, Co Roscommon, Mr Harris said: “What we have here is a random act. A violent act that has led to the death of Detective Garda Horkan.
“So it is tragic and it is an attack upon us all. Policing is an extension of good citizenship and we should acknowledge that this demeans and grieves us all as a society.”
Mr Harris added that Det Horkan was on a general anti-crime patrol at the time of the attack.
He added that it is difficult to say whether or not the suspect was known to Det Horkan given that he would have known many people in the local area due to his work.
A murder investigation has been launched after a garda detective was shot dead in Co Roscommon.
Detective Garda Colm Horkan, who had served with the Garda for 24 years, was killed in an incident in the town of Castlerea just before midnight.
A man in his 40s has been been arrested and is being held at Castlerea Garda Station.
It is understood that Horkan, who lived in Charlestown, was shot with his own weapon during a scuffle with a man close to the Garda station.
It is believed the officer had intervened in a incident unfolding on the street as he was returning to the station.
As the incident involved a Garda firearm, it has been referred to the Garda Siochana Ombudsman Commission.
The detective was originally from Co Mayo and is survived by his father, sister and four brothers, the Garda Representative Association said.
Gardai have closed the centre of Castlerea to traffic as investigations continue in the town of fewer than 2,000 people.
Detective Garda Horkan is the 89th member of the force to be killed in the line of duty.
