"People who cannot contain their urges to harm (or kill) people repeatedly for no apparent reason are assumed to suffer from some mental illness. However, they may be more cruel than crazy, they may be choosing not to control their urges, they know right from wrong, they know exactly what they're doing, and they are definitely NOT insane, at least according to the consensus of most scholars (Samenow 2004). In such cases, they usually fall into one of three types that are typically considered aggravating circumstances in addition to their legal guilt -- antisocial personality disorder (APD), sociopath, or psychopath -- none of which are the same as insanity or psychosis.
APD is the most common type, afflicting about 4% of the general population. Sociopaths are the second most common type, with the American Psychiatric Association estimating that 3% of all males in our society are sociopaths. Psychopaths are rare, found in perhaps 1% of the population."Nice distinctions of typology:
Antisocial Personality, Sociopathy, Psychopathy