A man raped, killed and mutilated a girl and pleaded diminished responsibility so that he should be guilty of manslaughter, not murder. The judge directed that if he was normal but on this occassion felt an abnormal sexual impulse that was hard to resist, the “diminished responsibility plea” did not apply. He was convicted of murder. Medical evidence said that Byrne was a sexual psychopath whose behaviour became impossible to control when driven by sexual desires, but not under normal circumstances. The Homicide Act 1957 says that the accused must show that he was suffering from an abnormality of mind which was induced by disease, injury retarded development etc, and was such that it impaired his mental responsibility for his acts in killing/ helping a killing. Appeal said that the defendant satisfied these conditions at the time of the murder and the trial judge’s direction was wrong.