Serotonin is a neurotransmitter that is linked with mood regulation. According to several studies, a decrease in levels of Serotonin may lead to aggression.
Impaired serotonin levels are found in many psychiatric conditions such as OCD, addiction, eating disorders, antisocial personality disorder and,etc.
Poor orbitofrontal cortex function is linked to lower levels of serotonin. This phenomenon is present in people with antisocial behavior.
Impulsive aggression is also linked with Low serotonin levels. Impulsive aggression is the key factor in violent and criminal behavior.
Not only the deficiency of serotonin makes one violent but other factors like social, cultural and economic causes plays important role. Although future research is needed to completely understand this phenomenon.