Garda Síochána informer Sean O'Callaghan claimed that Keenan recommended IRA Chief of Staff Seamus Twomey to authorise an attack on Ulster Protestants in retaliation to an increase in sectarian attacks on Catholic civilians by Protestant loyalist paramilitaries , such as the killing of three Catholics in a gun and bomb attack by the Ulster Volunteer Force on Donnelly 's Bar in Silverbridge , County Armagh on 19 December 1975 . According to O'Callaghan " Keenan believed that the only way , in his words , to put the nonsense out of the Prods Protestants was to just hit back much harder and more savagely than them " . Soon after the sectarian Kingsmill massacre occurred , when ten Protestant men returning home from their work were ordered out of a minibus they were travelling in , and executed en masse with a machine gun on 5 January 1976
Kingsmill massacre
Kingsmill massacre
Brian Keenan (Irish republican)