For many years, law enforcement and other officials have had problems with criminals and the inmates they control. People from all walks of life commit crimes. Some of these crimes are small and insignificant, others are gruesome and horrific. Violent offenders and nonviolent offenders have many similarities but also some differences. One major difference is that 80% of the two million people in jail and prison are men, and 80% of these are violent offenders (Lewis, 2010). This is the vast majority of criminals, and there are many more violent criminals than non-violent criminals. What personality traits are more evident in violent offenders than in nonviolent offenders? If there was a clear way to peer into the mind of a violent offender, it would have been done already. The importance of specifically identifying the personality traits of violent offenders is enormous. Research has shown that reduced functioning of central serotonin (5-HT) is related to impulsivity, aggression, and violent behavior (Retz, Retz-Junginger, Supprian, Thome, Rösler, 2004). This is important because if serotonin levels could be regulated, the level of aggression could be controlled. This would be very helpful to the rehabilitation efforts of the prison and prison officials. It is quite obvious that some personality traits are common in a violent person. Things like aggression and impulsivity are obvious, but others may not be. Things like psychopathic tendencies or even arrogant self-esteem and a feeling that the job is beneath them are also common. Among men who commit violent crimes, most meet the criteria for a conduct disorder by age 10 and have antisocial tendencies (...... middle of paper ...... erry, MP (1992 ) The Aggression Questionnaire. Journal of Personality and Social Psychology, 63, 452-459. Durose, Matthew R., Mumola, Christopher J. (2004) Profile of nonviolent offenders leaving state prisons. Hodgins, Sheilagh. (2007). Persistent violent offenders: what do we know? Behavioral Sciences and Law, 28(2), 224-234 doi:10.1002/bsl.929Retz, W., Retz-Junginger, P., Supprian, T., Thome, J ., & Rösler, M. (2004). Association of serotonin transporter promoter gene polymorphism with violence: relationship to personality disorders, impulsivity and psychopathology of childhood ADHD.589