He remains in custody at Castlerea Garda Station.
The man suspected of murdering Detective Garda Colm Horkan was known to Gardaí for his erratic behavior.
Detective Garda Colm Horkan lost possession of his gun during a physical altercation with a man on the main street of Castlerea Co. Roscommon on Wednesday night.
The man fired all 15 bullets in the gun, and Garda Horkan was hit multiple times, the 49-year-old Mayo native died at the scene.
A man in his 40s was arrested at the scene and brought to Castlerea Garda Station where he is being held.
The arrested man is known to Gardaí for his erratic behaviour and has mental health issues.
He is under constant surveillance as he attempted to injure himself in custody.
Books of condolence have opened at Garda Stations around the country today.
