As police search for a motive for Stephen Paddock’s massacre of dozens of people in Las Vegas this week, one detail shouldn’t come as a surprise—Paddock had a habit of berating his girlfriend in public.

While the motives behind mass shootings in modern American history vary, one thread connects them all: The perpetrators were overwhelmingly male and had a history of domestic abuse or misogynistic shows of behavior.

Omar Mateen, 29, who killed 49 people at the Pulse nightclub in Orlando in 2016, physically abused his former wife on a regular basis.

Seungh Hui Cho, 23, who gunned down 32 people at Virginia Tech in April 2007, was accused of harassing two women at the university two years earlier. Virginia police ordered him to stop contacting the second student.

Adam Lanza, 20, shot his mother four times before killing 20 children and six adults at Sandy Hook Elementary School in 2012.

George Hennard, 35, reportedly stalked two young adult sisters and wrote them a letter in which he called women “vipers” a few months before he murdered 14 women and 9 men at Luby’s Cafeteria in Killeen, Texas in 1991. The mass-murder was thought to be driven by his hostility towards women, and witnesses said he passed over men to shoot women.

Paddock, reports the Los Angeles Times, regularly demeaned his girlfriend in front of others at the local Starbucks, where they were regulars. “I’m paying for your drink, just like I’m paying for you,” Starbucks staff recalled him saying to Marilou Danley.

According to one study, in more than half of US mass shootings between 2009 and 2016, the killer (almost invariably male) shot a current or former intimate partner or a family member. Yet after a mass shooting, that link between domestic violence and gun violence usually gets overlooked: First there’s a heated debate on gun control. It’s big and angry, and goes nowhere. After that, details arise about the killer’s past history of abuse, and there are one or two laments about the link between domestic violence and mass-murder. And these will be largely ignored.

It happened after UC Santa Barbara. After Orlando. After Fort Lauderdale Airport. And, yes, after House majority whip Steve Scalise and four others were shot in June (paywall). Then? Nothing.

The link between domestic violence and gun violence

If the US won’t impose tighter gun control, perhaps it could take preventative action by paying attention to domestic violence.

Americans convicted of domestic violence are already banned from buying guns. But that didn’t stop the killers above. The US government needs to do much more, says Nancy Leong, law professor at the University of Denver: Before and during parole, she argues, known domestic-violence offenders should have their houses swept for any trace of firearms. There are precedents for this kind of monitoring: “A drug test looking at the interior of someone’s body is arguably more invasive than [searching] their house,” Leong says.

Even people who have merely been accused of domestic violence should have “extra scrutiny or delay associated with purchasing a gun,” she argues. According to US Bureau of Justice statistics, between 2006 and 2010, at least 46% of partner violence cases were not reported to police. An estimated one in four women in the US suffer domestic violence from a partner, and more from other men in their lives, and around 1 in 35 American women say a partner has threatened them with a gun.

The National Rifle Association might not like it, Leong acknowledges, but strict vetting is consistent with the exercise of other constitutionally-protected rights. “You need a permit to have a parade or a rally and exercise your first amendment rights,” she says. “This isn’t that hard.”

Beyond keeping guns away from domestic abusers, of course, far more needs to be done to stop domestic abusers in general. Leong puts this down to the attitude of the US criminal justice system, in which police and judges “tend to treat things like domestic violence as less serious than other kinds of crimes,” she says, and don’t use all the discretion they have to punish perpetrators. “Really, just treating the behavior involved in domestic violence like other crimes of comparable severity would already be a step in the right direction.”

Heather Timmons and Annalisa Merelli contributed to this report.

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