Psychopathic behaviour seems to be linked to an imbalance in brain chemicals, according to a new study.
Swedish researchers discovered that men with psychopathic tendencies also had high levels of a brain chemical responsible for aggression.
The men also had low levels of another chemical which normally helps regulate the aggression chemical, causing the imbalance.
The psychopathic personality is characterised by inconsistent impulsive behaviour and a tendency to dominate others using violence and aggression.
The new findings are based on studies of 28 men who had all committed violent crimes including murder, attempted murder, aggravated assault, arson, rape and sexual assault of children.