The psychological and forensic profile of men who murder their intimate partners varies from murderers who kill people they don’t know, a study published online Friday in the Journal of Forensic Sciences suggests. 

The study, conducted by scientists at Northwestern University, involved more than 1,500 hours of interviews with 153 male and female murderers charged with and/or convicted of first-degree murder in Illinois, Missouri, Indiana, Colorado and Arizona.  

“You learn a lot about them in that amount of time,” lead author Robert Hanlon, director of the forensic psychology research lab at Northwestern University Feinberg School of Medicine, said in a news release. “I saw the same patterns and trends over and over again.”

“The findings provide important information that may help prevent future domestic homicide because they help identify individuals at risk of committing domestic murders, added Hanlon, who is also an associate professor of psychiatry and behavioral sciences at Feinberg and a neuropsychologist at Northwestern Memorial Hospital, and who testified in the James Holmes Colorado theater mass murder trial in Denver in July. “The killers in this group are very similar to each other and different from men who commit nondomestic murders, which are often premeditated.”

According to the news release, one-third of women murdered in the United States are killed by their male husbands, ex-husbands, boyfriends and ex-boyfriends. About 25 percent of women will suffer severe domestic violence from an intimate partner during their lifetimes.

The study found that killers involved in spontaneous domestic homicides are more likely to have severe mental illness, few previous felony convictions, less intelligence and more cognitive impairment compared to murderers who don’t know their victim.

“These crimes are often preventable if family members are more informed about the potential danger from having someone who is severely mentally ill in the home and who may have shown violent tendencies in the past,” Hanlon said. “Family members may lull themselves into a state of false beliefs thinking ‘my son would never hurt me’ or ‘my husband may have a short fuse but he would never seriously harm me.’”

“The fact is the husband or son may very well harm the wife or mother,” Hanlon said.

He noted that common factors in spontaneous domestic murders were drugs, alcohol and a motive concerning jealousy or revenge after a breakup.

“This is grabbing the kitchen knife out of the drawer in a fit of anger and stabbing her 42 times,” he said.

Halon advised intimate partners and family members to notify police and get themselves to a safe place if they feel they may be in harm’s way.

“You can stay with relatives, call domestic violence hotlines and say, ‘I’m scared something is going to happen to me,’” Hanlon said. “Start the wheels turning and get assistance.”