A new study published in Criminal Justice and Behavior shows that those who commit premeditated murder are usually not cognitively impaired and their minds are actually quite different from those who impulsively kill.
In fact, the most marked difference the study found was that most impulsive killers do not suffer from serious mental illness, but instead are usually just mentally impaired through a lower intelligence quotient (IQ) and/or learning disability.
The study was lead by associate professor of clinical psychiatry and clinical neurology Dr. Robert Hanlon of the Northwestern University Feinberg School of Medicine.
Difference between premeditated and impulsive murderers
The main finding was that premeditated murderers usually suffer from the same types of psychotic or mood disorders in a far narrower window of classification than many believed. Impulsive killers were nearly twice as likely to have low IQ or developmental disabilities rather than an illness.
The study examined 77 murderers incarcerated in either Illinois or Missouri. They were all given standardized intelligence and neuropsychological memory tests. This is the first study to examine these differences between murders who kill impulsively versus those who killed strategically.
It's important to remember that the mentally ill are far more likely to be the victims of violence than the perpetrators of it, including murder.
