Inside the Mind of Premeditated Murder: Links to Common Signs of Mood or Psychotic Disorders

Intense situations and emotions can cause people to do crazy things. For instance, a mother catching the site of her child in danger can give her the adrenaline boost to put herself in the same threatening circumstance in the hopes of rescuing her child. However, that same adrenaline rush in a dangerous or difficult situation can cause some people to kill someone or even commit murder.

According to a recent study conducted by Northwestern Medicine, researchers examined the minds of murderers who kill impulsively, often out of rage, versus premeditated plans.

"Impulsive murderers were much more mentally impaired, particularly cognitively impaired, in terms of both their intelligence and other cognitive functions," said Hanlon, senior author of the study and associate professor of clinical psychiatry and clinical neurology at Northwestern University Feinberg School of Medicine, via a press release. "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 examined the neuropsychological and intelligence differences of murderers who kill impulsively versus those who kill as a result of a strategic plan. It examined 77 murderers from typical prison populations in Illinois and Missouri who were classified into two groups: Affective/impulsive and premeditated/predatory murderers. The results note the following, courtesy of the release.

• 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.

"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."

More information regarding the study can be seen online in the journal Criminal Justice and Behavior.