Just because he’s a psychopath, doesn’t mean he’s guilty

The media is awash, it seems, with stories about psychopaths. Whether it's the latest fictional crime drama, or the recent Netflix series on serial killer Jeffrey Dahmer, those with the psychological disorder of psychopathy are a group we seem to love to hate.

That's one thing watching TV, but what happens in a court case when a psychologist has assessed a defendant as having psychopathy? Is the jury going to be more likely to give a guilty verdict, irrespective of the facts of the crime? New research seems to suggest that may well be the case.

For the study, 168 participants were given four short stories (vignettes) about a crime, and were asked to decide whether they thought the defendant was guilty, and why.  Two of the vignettes described an assault by a man against another man, and included a psychologist's assessment, one describing the offender as a psychopath and the other reporting no psychological difficulties or disorders.

The second two vignettes described a case of robbery. However instead of a psychological assessment they contained character witnesses, with one defendant described as narcissistic, manipulative, aggressive, egotistical and lacking remorse, and the other as a friendly, kind and caring person.

After reading all four vignettes, participants completed a questionnaire specially designed to measure their bias towards a particular group, in this case those with psychopathic traits.

The results were stark. Most participants adjudged the psychopathic character guilty more often than the non-psychopathic character, and most deemed the character with psychopathy traits guilty more often than the character without them. This is despite the evidence given against the defendants in the stories being almost identical. Moving onto the questionnaire, most respondents were found to have negative beliefs and an active bias towards those with psychopathic tendencies, despite having little understanding of what psychopathy is and how it affects people.

Some participants were very clear about their bias. One stated that the person "doesn't recall their actions which could be due to his psychopathy". Similarly, those who gave a guilty verdict on the basis of the psychopathy description often justified it due to "a tendency of being aggressive". One respondent suggested the "crime fit with his persona" and another gave the character witness as the reason they believed the person was guilty.

Moving to the defendant with a 'clear' psychopathic assessment, the participants were much less sure about guilt. Some stated that "no disorders" and "the psychologist's report" were reasons for a not guilty verdict, whilst many others shifted from a certainty of guilt with the psychopath label to an unwillingness to give that verdict without it. 

Similarly, for the character without the psychopathic descriptors, respondents often cited not having enough evidence for a verdict, or reporting the defendant "wouldn't do such a thing based off the character witness". More than anything, says the study, these responses illustrate just how important character witness statements are with regard to verdicts in legal cases.

The study's author, clinical psychologist Jacob van Bentum, is clear about the real-world implications of these findings:

"The results from this study could have major ramifications for the validity and fairness of the criminal justice system. Our results suggest that character statements, whether positive or negative, can sway a lay person's opinion, despite the fact they have no bearing on the facts of the crime. Moreover, exaggerated use of psychopathy labels could potentially lead to biased and false convictions. My hope is that the study, once expanded, will lead to recommendations to reduce the influence of this bias on our legal system."

The full study, 'Investigating the presence of psychopathy bias in the general population and its impact on judgements of guilt', can be read in the latest edition of Assessment and Development Matters via BPS Explore.