The Garda Commissioner, the President and the Taoiseach have been leading the tributes to Detective Garda Colm Horkan.
He has been described as an experienced detective who was greatly respected.
President Michael D Higgins says the death of a detective garda while on duty has shocked us all while Taoiseach Leo Varadkar said his thoughts are with all those grieving as a result of the shooting.
Garda Commissioner Drew Harris said Detective Garda Colm Horkan served the communities he worked in with distinction and pride during his 24 years as a garda.
Last night Detective Garda Colm Horkan was on patrol in Castlerea when he went to deal with something on the main street.
The situation evolved into a physical altercation and he was shot dead with his own gun.
Emergency services treated him at the scene but sadly Gardaí confirmed early this morning that Detective Horkan had died.
He was in his late 40s and has served as a Garda for 24 year. He’s survived by his parents, sister and four brothers.
A man in his 40s has been arrested and is being questioned at Castlerea Garda Station.
The Garda Commissioner Drew Harris has made a direct appeal for witnesses to come forward.