psychopath

A person with a personality disorder indicated by a pattern of lying, cunning, manipulating, glibness, exploiting, heedlessness, arrogance, delusions of grandeur, carelessness, low self-control, disregard for morality, lack of acceptance of responsibility, callousness, and lack of empathy and remorse. Such a person may be especially prone to violent and criminal offenses.

A person who perpetrates especially gruesome or bizarre violent acts.