Predatory killers often do far more than commit murder. Some have lured their victims into homemade chambers for prolonged torture. Others have exotic tastes - for vivisection, sexual humiliation, burning. Many perform their grisly rituals as much for pleasure as for any other reason. Among themselves, a few forensic scientists have taken to thinking of these people as not merely disturbed but evil. Evil in that their deliberate, habitual savagery defies any psychological explanation or attempt at treatment. Most psychiatrists assiduously avoid the word evil, contending that its use would precipitate a dangerous slide from clinical to moral judgment that...