Mass shootings in the United States are a tragically common occurrence. In fact, 31 percent of the world’s public mass shootings over the last four decades have taken place in the U.S. Perhaps even more shocking, the majority of mass murders in the U.S. occur in private. Familicide—the murder of an entire family by one member—occurs roughly 23 times every year in this country. New research shows that people who kill family members in fits of domestic violence have a unique criminological profile, compared to those who murder strangers and non-family members.
Intimate partner homicides are not unique to the U.S. “Domestic violence is a global epidemic,” says Robert Hanlon, a clinical neuropsychologist at Northwestern University’s Feinberg School of Medicine and lead author on the new study. “Half of all female murder victims in Europe were killed by intimate partners or other relatives … that’s even more than the U.S. where a third of all female murders are domestic homicides.”
The killers who committed spontaneous domestic murders had lower IQ scores and greater deficits in attention, memory, and other executive—or self-regulatory—functions.
To find out how those who commit domestic murders differ from other killers, the researchers interviewed 153 men and women across Illinois, Missouri, Indiana, Colorado, and Arizona who’d all been charged with or convicted of murder in the first-degree (meaning willful and pre-meditated). Hanlon and his colleagues assessed the cognitive abilities of the murderers—one-third of whom committed spontaneous domestic homicides, while nearly two-thirds committed non-domestic murders—and reviewed their criminal, medical, psychiatric, and student records.
The team found that the killers did share some traits: Violent histories, illicit drug use, and psychotic disorders were common among both sets of murderers, and a shocking majority—nearly 84 percent—had suffered at least one incident of head trauma. But while both groups showed signs of cognitive impairments, the killers who committed spontaneous domestic murders had lower IQ scores and greater deficits in attention, memory, and other executive—or self-regulatory—functions.
This unique criminological profile could be used to inform the public about the risk of domestic violence, according to Hanlon, who says that a history of violence; a major life stressor, such as the loss of a job; and a serious mental illness all increase the chances that an individual will unleash their anger on a family member. However, Hanlon cautions, while mental illness is a risk factor, it is certainly not the whole story. Millions of people suffering from mental illnesses are non-violent, and many are actually more vulnerable to being victims of violence than perpetrators, he says. Rather, stressful life events, head trauma, and poor impulse control can compound mental illness, manifesting in violent outbursts.
“If you then add into the mix some substance abuse—so you throw in alcohol and/or drugs on top of that,” Hanlon says, “that, then, is a formula for domestic violence.”
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