"Psychologists and psychiatrists have long tried to understand the roots of psychopathy, proposing an assortment of moral or emotional deficits to account for the psychopath’s callousness. To explain their impulsiveness, researchers argue that psychopaths lack anxiety, foresight or self-control. These deficiencies leave them unconcerned about the future consequences of their behaviour or unable to restrain their urges."

 

http://www.iflscience.com/brain/why-violent-psychopaths-don-t-get-punishment