June 28, 2013, 12:41 PM —
Image credit: Flickr/Alan Cleaver
All murderers have an important and obvious thing in common: They have deliberately taken at least one human life. But researchers are discovering vast differences between the minds of impulsive killers and premeditated murderers.
"Impulsive murderers were much more mentally impaired, particularly cognitively impaired, in terms of both their intelligence and other cognitive functions," said Robert Hanlon, associate professor of clinical psychiatry and clinical neurology at Northwestern University Feinberg School of Medicine.
Hanlon is the lead author of a study published in the online journal Criminal Justice and Behavior. The research team examined neuropsychological and intelligence differences between impulse killers and those who murder as the result of a premeditated plan.
Among the findings:
* Compared to impulsive murderers, premeditated murderers are almost twice as likely to have a history of mood disorders or psychotic disorders -- 61% versus 34%.
* Compared to predatory murderers, impulsive murderers are more likely to be developmentally disabled and have cognitive and intellectual impairments -- 59% versus 36%.
* Nearly all of the impulsive murderers have a history of alcohol or drug abuse and/or were intoxicated at the time of the crime -- 93% versus 76% of those who strategized about their crimes.
What I find interesting in the data above is that premeditated murderers are more likely to have mood and/or psychotic disorders. I would have expected impulsive murderers to be more burdened by mood and psychotic issues.
Hanlon's team studied 77 murderers from prisons in Illinois and Missouri, administering tests for intelligence, memory, attention and other neuropsychological factors.
By studying the minds of murderers, Hanlon says, "We may be able to increase our rates of prevention and also assist the courts, particularly helping judges and juries be more informed about the minds and the mental abnormalities of the people who commit these violent crimes."