The study reveals a surprising level of heterogeneity in psychopathy among convicted capital murderers

New research sheds light on the psychological profiles of individuals convicted of capital murder in California and sentenced to death. The study, published in Journal of Forensic Sciences, found a “pronounced heterogeneity” regarding clinical psychopathy. While a significant proportion of offenders showed enhanced psychopathic traits, others showed no signs of psychopathy.

Psychopathy is considered important to understanding criminal behavior because it is a personality disorder characterized by a lack of empathy and remorse, along with impulsive and reckless behavior. Research has shown that people with psychopathic traits are over-represented among offenders, particularly those who have committed violent or repeat offences.

Understanding the traits and behaviors associated with psychopathy can help predict and prevent criminal behavior, as well as the development of more effective treatment and rehabilitation programs for offenders.

“Psychopathy and homicide are two of my research areas, so the current study combines them using a very unique data source,” said study author Matthew J. Delisi, a distinguished professor, dean professor and coordinator of criminal justice at Iowa State University.

For their study, the researchers examined data from the Death Row Tracking System maintained by the California Department of Corrections and Rehabilitation Division of Adult Operations. The selection included 636 people convicted of capital murder and sentenced to death. The data included information on the offender’s psychopathology, personality functioning, offending history and involvement in the criminal justice system.

“The data took three years to collect,” noted Delisi, the author of “Ted Bundy and The Unsolved Murder Epidemic: The Dark Figure of Crime.”

The offenders showed many aggravating circumstances related to their murder cases, such as kidnapping, rape/sexual assault, armed robbery and torture. The most common manner of death was shooting with a firearm, followed by stabbing with a bladed weapon and manual strangulation. The sample was racially and ethnically diverse (38% African American, 36% White, 24% Hispanic, and 2% Asian or Native American), but overwhelmingly male (97.3%).

The researchers used the Hare Psychopathy Checklist-Revised (PCL-R) to assess psychopathy. It is a 20-item questionnaire administered by trained professionals and scored based on a subject’s file information and an interview. The items on the checklist are designed to measure the presence of certain personality traits and behaviors associated with psychopathy, such as lack of remorse, manipulation, and impulsivity.

PCL-R scores range from 0 to 40. A score of 30 or higher corresponds to a diagnosis of psychopathy. For the current study, the researchers scored offenders based on information in their legal documents, as it was not possible to conduct an interview.

Delisi and his colleagues found a surprising level of heterogeneity. The average PCL-R score for the sample was 23.31, indicating that the “average killer on California’s death row is moderately psychopathic,” Delisi told PsyPost.

But nearly 15% of the sample had PCL-R total scores below 10. “Some of these offenders had no official criminal history prior to their capital crimes, were contrite, apologetic, and remorseful during court proceedings, and generally engaged in normative behavior,” the researchers said.

On the other hand, one third of the offenders met the diagnostic threshold for clinical psychopathy. “To put this into perspective, <1% of those in the general population meet diagnostic thresholds for clinical psychopathy, and the majority of the general population does not display a single psychopathic trait," the researchers explained. Clinical psychopathy is over 50 times more prevalent among these individuals convicted of capital murder and sentenced to death compared to studies of individuals in the general population.”

“There is a lot of diversity in psychological functioning among death row inmates,” Delisi explained. “Some do not have a single trait of psychopathy, others are complete psychopaths.”

The researchers also found that psychopathy was associated with several other psychiatric conditions. Highly psychopathic offenders were much more likely to also show signs of conduct disorder and antisocial personality disorder and slightly more likely to show signs of ADHD, Oppositional Defiant Disorder, and sexual sadism compared to their less psychopathic counterparts.

“More psychopathic killers had more severe psychopathology,” Delisi said.

Psychopathy was also positively related to the number of arrests, prison sentences and age of arrest, showing that the condition “is closely related to the severity of criminal careers.” In other words, psychopathic offenders “had earlier started and more extensive criminal careers,” Delisi explained.

The study, “Psychopathy among convicted capital murderers,” was written by Matt DeLisi, David J. Peters, Andy Hochstetler, H. Daniel Butler, and Michael G. Vaughn.

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