Study casts doubt on idea that murderers are particularly psychopathic

What do you think characterises the personality of a murderer? Going by countless TV shows, podcasts and books — not to mention studies linking certain personality traits to callous, violent acts — you'll probably think: psychopathy.

However, actual scientific research into this has been astonishingly slim on the ground. And now a study of prisoners in Serbia reports that, in fact, murderers have less in the way of psychopathic (and also sadistic) traits than other kinds of criminal.

Janko Međedović and Nikola Vujičić of the Institute of Criminological and Sociological Research in Belgrade studied 247 male convicts who were serving time in two of the biggest penitentiaries in Serbia. Of this group, 46 were murderers, 82 had committed non-homicide violent offences (mostly violent robberies and grievous bodily harm) and 119 were non-violent offenders (convicted for dealing drugs, for example).

The participants completed questionnaires that assessed their levels of psychopathy, sadism and also Machiavellianism. For each criminal, the team looked at these results and also details of their past history, if any, of offending.

Their main result was that murderers had lower levels of both psychopathy and sadism than the other types of offenders (there was no difference in levels of Machiavellianism). This was particularly true when the murderers were compared with the violent non-murderers.

But even when they were held up against both of the other criminal groups, they had lower levels of sadism and also lower scores on two characteristics of psychopathy: "lifestyle" (a measure of social deviance) and being "antisocial" (a measure of aggressive antisocial behaviour). "Our data cast a doubt on the widely acknowledged link between psychopathy and murder," the team concludes.

The murderers also had less of a track record of offending. This fits with an earlier finding that almost 40% of "multiple homicide offenders" (a group that includes serial killers), had not been arrested for anything at all before committing murder. 

Why might murderers be less likely to be psychopaths than other types of criminal? The researchers suggest that while people high in psychopathy are more likely to commit a crime, murder is a special case. Yes, psychopathy has been linked to certain types of murder, especially the premeditated murder of a stranger or slim acquaintance. But most murders don't fall into this category. People kill others for all sorts of "reasons", from injured pride to a desire for revenge — and don't, it seems, need a high level of psychopathic or sadistic traits to be capable of doing this.

"While we agree that dark traits may be associated with some types of murder, we think that this link cannot be established for murder in general."

Still, there are some limitations to the study that are worth noting. The team did not include a comparison group from the general population. So of course murderers may well have higher levels of psychopathic traits than the typical person — just not as high as the other types of criminal.

Also, the sample sizes of murderers and non-homicide violent offenders were quite small (with greater numbers, it's possible that a different pattern of results might have emerged); the dark traits were only self-reported (and so not objectively verified); and as the study didn't involve women, the findings obviously apply only to men.

As the team notes, they didn't have information on what type of homicide the murderers had committed — whether it was of a spouse, say, or in the course of a gang fight, perhaps. They acknowledge that this information would have been useful for a study of links between dark traits and homicide. But, they add, to get sufficient participants for a decent analysis, that kind of work might have to be done in a country bigger than Serbia.

For now, the team highlights this interesting conclusion: "While we agree that dark traits may be associated with some types of murder, we think that this link cannot be established for murder in general."