Serial Killer Psychology

By William R. Harris

Criminal psychology refers to the study of the mental and behavioral characteristics of people who break laws established by local, state, national or international governments. Some criminal, or forensic, psychologists focus their research on serial killers -- men and women who murder a large number of people over an extended period of time — typically months or years.

What constitutes a serial killer is open to interpretation. In the United States, Congress has defined a serial killer as someone who murders a minimum of three or more people. By definition, a cooling-off period separates the murders, making them appear random or unconnected. The victims — often prostitutes, runaways or other vulnerable populations — rarely know their killer and may serve as a symbol that triggers the attack. In other words, a serial killer's motive tends to be psychological, not material.

Understanding what goes on — or gets turned off — in a serial killer's mind is the ultimate goal of scientists who specialize in this area of psychology. You might think the field is relatively new, but it dates back to at least the 19th century, when psychologists tried to develop a profile of the mysterious and elusive Jack the Ripper.

Antisocial Personality Disorder vs. Psychopathy

Mental health professionals use the Diagnostic and Statistical Manual of Mental Disorders (DSM), developed by the American Psychiatric Association, to understand the illnesses of their patients and how to treat them. The DSM doesn't list serial murder among the 300 known mental disorders catalogued in its pages. It does, however, describe antisocial personality disorder, or ASPD. It's this condition that describes the behavior of many serial killers.

To understand ASPD, it helps to review the DSM criteria used to diagnose it. The most obvious indicator of the disorder is a total disregard for laws and social norms. People with ASPD have a long history of arrests and are often involved in physical fights or assaults. Some are capable of lying, cheating and deceiving so skillfully it is difficult to know when they are telling the truth or lying. They also act impulsively, with little care given to the safety of themselves or others.

To be diagnosed officially with ASPD, a person must be 18 years old, but symptoms generally begin to appear earlier, sometimes in the early teens. Adults with ASPD struggle to stay employed and, as a result, often have financial problems, according to the DSM. The manual also mentions that the disorder occurs more frequently in men than women — about 3 percent versus 1 percent.

Experts describe psychopathy as a more severe form of ASPD. Psychopaths have the antisocial symptoms just mentioned, but they also have additional traits that make them especially difficult to diagnose and treat. Chief among these traits is a lack of remorse or guilt for their actions. They also tend to be highly paranoid and suspicious.

Robert D. Hare of the University of British Columbia, a pioneer in the field, developed a diagnostic tool for psychopathy that measures the same antisocial symptoms as the DSM, but also evaluates interpersonal criteria, such as lack of empathy and shallow emotions. The tool is known as the Hare Psychopathy Checklist — a collection of 20 criteria that measure a person's antisocial behavior, emotional and interpersonal traits, and other factors.

The highest possible score is 40, but someone who scores 30 points is considered a psychopath, according to Kent Kiehl and Joshua Buckholtz, who explored the mind of a psychopath for Scientific American. Interestingly, the average score on the Hare Psychopathy is 4, write Kiehl and Buckholtz. That just means that psychopathy is a continuum, the way many other disorders are. It also means most psychopaths are not violent and are not destined to commit murder. A few, however, fall at the far end of the scale. These violent psychopaths may include serial killers.

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