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Men who murder their wives or girlfriends are a distinctly different group than those who kill strangers, according to a new study by a forensic psychology research lab at Northwestern University. Chief among those differences: they are less likely to have a rap sheet for serious crimes.

The murderer in a domestic homicide is also more likely to have a psychotic disorder, "but less likely to be diagnosed with an antisocial personality disorder or to have prior felony convictions," wrote lead author Robert Hanlon in a paper published Aug. 21 in the online edition of the Journal of Forensic Sciences. Hanlon testified in the trial of James Holmes, recently convicted in the Colorado movie theater mass killing.

[Retraction watch: Marriages fail more often when wife falls ill]

Compared to those who kill strangers -- crimes that are often premeditated -- men who commit spontaneous domestic and intimate-partner homicide are usually less intelligent, have poorer attention and have greater impairment in executive functioning, such as controlling their impulses. All these deficits characterized both groups of killers but were demonstrably worse in domestic murderers. More than 80 percent of the latter group also had a history of head trauma, and 78 percent had a lifetime history of illicit drug abuse.

More than 60 percent of the domestic killers had used drugs or alcohol during the commission of their crimes.

Domestic violence is considered a preventable public health problem that affects millions of Americans every year, with a one-in-four lifetime chance of a woman being the victim of intimate-partner violence, according to the National Institute of Justice. More than 30 percent of murder victims are killed by someone they know, according to statistics in the Federal Bureau of Investigation Uniform Crime Report.

[Aurora movie theater gunman sentenced to life in prison without parole]

Hanlon, who also is an associate professor of psychiatry and behavioral sciences at Northwestern's Feinberg School of Medicine, interviewed and evaluated 153 murderers -- more than 88 percent of them male -- for more than 1,500 hours. All had been charged with and/or convicted of first-degree murder in five states (Arizona, Colorado, Illinois, Indiana and Missouri) and were referred for neuropsychological evaluation for fitness to stand trial, criminal responsibility or sentencing.

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