Joe Tiernan suggested that Jackson killed Hanna on account of the latter 's refusal to participate in the Miami Showband killings . Hanna apparently suffered remorse following the 1974 Dublin bombings , as he is believed by Tiernan to have instructed one of the bombers , David Alexander Mulholland to drive the car which exploded in Parnell Street , where two infant girls were among those killed . According to Tiernan and the '' Barron Report '' , David Alexander Mulholland was identified by three eyewitnesses . Tiernan also suggested that Hanna and Mulholland became informers for the Gardaí regarding the car bombings in exchange for immunity from prosecution . He added that although the British Army was aware of this , Jackson was never told , as it was feared he would decide to become an informer himself
1974 Dublin bombings
Dublin and Monaghan bombings
Robin Jackson