Derek Mulligan (39), with an address at Carrickcoyle, Derrybeg, Gweedore in Co Donegal has pleaded not guilty by reason of insanity to the murder

A prosecuting barrister told the trial of Derek Mulligan on Monday that the accused was the victim of serious sexual abuse at the hands of a school caretaker when he was a child and has suffered with a litany of mental health difficulties since his teenage years.