This post is entirely originating from "The Serial Killer Files: the who, what, where, how and why of the world's most terrifying murders" from Harold Schelchter that I can only recommend to everyone. In his book, Harold Schlechter refers to a conference given by Robert Ressler and John Douglas (two notorious FBI special agents from the Behavioral Science Unit and pillars of offender profiling) during the 10th Triennal Meeting of the International Association of Forensic Sciences held at Oxford, England, in September 1984. These traits are the result of their study and analysis of 36 jailed offenders.
1) Most are single white males.
2) They tend to be smart, with an IQ of "bright normal".
3) Despite their intelligence, they do poorly in school, have spotty employment records, and generally end up as unskilled workers.
4) They come from deeply troubled families. Typically, they have been abandoned at an early age by their fathers and grow up in broken homes dominated by their mothers.
5) There is a long history of psychiatric problems, criminal behaviors and alcoholism in their families.
6) As children, they suffer significant abuse - sometimes psychological, sometimes physical, often sexual. Such brutal mistreatment instills them with profound feelings of humiliation and helplessness.
7) Because of their resentment toward their distant, absent, or abusive fathers, they have a great deal of trouble with male authority figures. Because they were dominated by their mothers, they have a powerful hostility towards women.
8 ) They manifest psychiatric problems at an early age and often spend time in institutions as children.
9) Because of their extreme social isolation and a general hatred of the world and everyone in it (including themselves), they often feel suicidal as teenagers.
10) They display a precaucious and abiding interest in deviant sexuality and are obsessed with fetishism, voyeurism, and violent pornography.
These traits represent a general image of serial killers, but it does not mean that every single serial killer presents these traits, nor that people who present these traits are or will be serial killers.