O'Callaghan claimed to have been tasked in 1983 by the IRA with placing 25lb of Frangex in the Dominion Theatre in London, to try to kill Prince Charles and Princess Diana who were due to attend a charity pop music concert there. A warning was phoned into the Garda, and the Royal couple were hurriedly ushered from the theatre by their police bodyguard during the concert. The theatre had been searched before the concert and a second search following the warning revealed no device.