A paper was published in Brain Imaging and Behavior which found reduced gray matter--areas of the brain that are associated with emotional processing, behavioral control, and social cognition--in people convicted of homicide compared to non-homicide offenders.
The study examined the brain scans of incarcerated adult males who had committed homicide and compared them to prisoners that had committed other non-violent crimes.
For the first time, it was demonstrated that there may be unique brain abnormalities that distinguish offenders who kill from other violent offenders as well as non-violent individuals.
The study, it is important to note, implies correlation, not causation.
Read the published paper in Brain Imaging and Behavior.