[1][2] Donegan joined the Garda Síochána, the Republic of Ireland's police force, at the age of 23, on 4 September 1934, being issued with the Service No.
[1] On 8 June 1972, Inspector Donegan was leading a Garda patrol in conjunction with an Irish Defence Force detachment on the border between County Cavan, part of the Republic of Ireland, and County Fermanagh, part of Northern Ireland.
In the Drumboghanagh neighbourhood,[3] very near Wattlebridge, a few miles south of Newtownbutler, they found a tea-crate apparently abandoned in the road painted with comical style lettering saying "BOMB!
Further along the Drumboghanagh Road, a country lane, the patrol found a second identical tea-crate, which suddenly detonated whilst they were examining it, killing Donegan.
[1][4] In January 2013, Sinn Féin President Gerry Adams issued a statement in which he apologised on behalf of the IRA to the families of Gardaí and the families of all members of State forces injured or killed by the Provisional IRA, but denied knowledge of who was responsible for planting the bomb that had killed Inspector Donegan.