Murder is front-page news, and a new study discovers significant mental differences among premeditated and impulsive killers.
As published online in the journal Criminal Justice and Behavior, Northwestern Medicine researcher Robert Hanlon, Ph.D., found that the minds of murderers who kill impulsively, often out of rage, and those who carefully carry out premeditated crimes, differ markedly both psychologically and intellectually.
“Impulsive murderers were much more mentally impaired, particularly cognitively impaired, in terms of both their intelligence and other cognitive functions,” said Hanlon.
“The predatory and premeditated murderers did not typically show any major intellectual or cognitive impairments, but many more of them have psychiatric disorders,” he said.
The study is the first to examine the neuropsychological and intelligence differences of murderers who kill impulsively versus those who kill as the result of a premeditated strategic plan.
Among its findings:
- Compared to impulsive murderers, premeditated murderers are almost twice as likely to have a history of mood disorders or psychotic disorders — 61 percent versus 34 percent.
- Compared to predatory murderers, impulsive murderers are more likely to be developmentally disabled and have cognitive and intellectual impairments — 59 percent versus 36 percent.
- 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 percent versus 76 percent of those who strategized about their crimes.
For the research, 77 murderers from typical prison populations in Illinois and Missouri were classified into the two groups (affective/impulsive and premeditated/predatory murderers).
Hanlon compared their performances on standardized measures of intelligence and neuropsychological tests of memory, attention and executive functions.
He then spent hours with each individual, administering series of tests to complete an evaluation.
“It’s important to try to learn as much as we can about the thought patterns and the psychopathology, neuropathology and mental disorders that tend to characterize the types of people committing these crimes,” he said.
“Ultimately, 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.”
Source: Northwestern University