In 2016, there were an estimated 17,250murders in the United States.

Homicide, of course, has a devastating impact on individuals and society at large.

As such, it is essential to study the biological, psychological, and social basis of these terrible acts.

Although earlier studies have looked at how a murderer's brain might differ from that of a non-murderer, they have often been flawed.

A group of scientists recently set out to fill in some of the gaps, and they designed the largest study of its type, to date. The researchers have published their findings in the journal Brain Imaging and Behavior.

Flaws in earlier work

Earlier studies using PET scans, carried out in the 1990s, concluded that homicide offenders' brains demonstrated reduced activity in a number of brain regions.

These include parts of the prefrontal cortex — which is a region that is important for moderating social behavior, among many other things — and the amygdala, which plays a vital role in processing emotions.

Although the findings were interesting, the researchers had exclusively enrolled participants who had been found "not guilty by reason of insanity." Therefore, any of the differences that the scientists measured could have been due to mental illness or brain injury, rather than homicidal tendencies.

Other, later studies have investigated the brains of violent individuals with conditions such as schizophrenia. These researchers have found changes in similar brain regions, but they face the same issues. As the authors of the new study explain:

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