DENVER — What do many mass shooters have in common? A history of domestic violence.

At first glance, mass shooters like James Hodgkinson, who authorities say opened fire Wednesday morning as Republicans practiced for the Congressional Baseball Game, seem like a diverse group.

Hodgkinson, whose attack injured House Majority Whip Steve Scalise, a congressional aide, a lobbyist and two Capitol Police officers, had frequently criticized President Trump and other Republican leaders on social media and in letters to his local newspaper, and had contacted the office of Rep. Mike Bost, R-Ill., 14 times to criticize Republicans.

Past mass shooters have chosen targets or left manifestos indicating wildly different possible political beliefs or motivations – or given no indication at all about what made them act. With no common ideology or goal uniting the perpetrators of such horrific violence, how can we identify those likely to perpetrate mass shootings and prevent them from doing so?

There is one thing, though, that an alarming number of the recent mass shooters in the U.S. share: A history of aggression and violence toward women.

• Seung-Hui Cho, who killed 32 people in the horrific massacre at Virginia Tech in 2007, had been previously investigated for stalking two female classmates.

• Elliot Rodger, who killed six and wounded 13 in Isla Vista, California, in 2014, was obsessed with perceived rejection by women, and not long before the shooting had thrown coffee on two women at a bus stop because they didn’t smile at him.

• Ismaaiyl Brinsley, who murdered two police officers in Brooklyn, New York, in 2015, shot his ex-girlfriend in the stomach just hours earlier.

• Cedric Ford, who shot 17 people last year at the Newton, Kansas, plant where he worked, killing three, had been accused of abusing his ex-girlfriend and served with a restraining order not long before the shooting.

• Robert Dear, who shot and killed three people at a Planned Parenthood in Colorado Springs, in 2015, had a history of domestic violence.

• Omar Mateen, who murdered 49 people at the Pulse nightclub in Orlando, abused his wife for years, beating her because she had not finished the laundry or a similar offense.

Hodgkinson fits the same pattern. In 2006, police records show, Hodgkinson went to his neighbor’s house looking for his daughter and forced his way into the home, using “bodily force to damage” a door. According to a police narrative on file with the St. Clair County, Illinois, Sheriff’s Department, witnesses said he grabbed his daughter by the hair, chased her to their neighbor’s car and used a knife to cut her seat belt off so he could pull her out. Police records say he also punched his neighbor in the face after she told him she would call 911.

The incident did not result in punishment within the legal system. Hodgkinson appeared in court and had screaming outbursts that caused him to be removed. Nonetheless, the judge apparently dismissed his case after a witness accidentally failed to appear at a rescheduled hearing. “I tried to tell the court that this guy’s crazy, that this is a big deal, but they didn’t listen to me,” the neighbor said.

One analysis of mass shootings from 2009 through 2016 concluded that at least 54 percent of mass shootings – or 85 out of 156 incidents – involved a current or former intimate partner or family member as a victim.

Of course, it shouldn’t be a surprise that domestic violence and mass shootings are correlated. People who are likely to act violently often start with those nearest to them, who are vulnerable because of proximity and who are often financially, emotionally or legally dependent on their abuser.

The justice system also plays a role, treating domestic violence with less weight than “real” violence. Abusers are less likely to be incarcerated for a domestic violence incident than for an incident involving violence against someone other than a family member or an intimate partner, and are thus less likely to undergo the type of intensive rehabilitation that might deter violence in the future.

Despite research documenting a connection between domestic violence and mass shootings, we still don’t focus on domestic violence enough in the wake of such a shooting. A mass shooting tends to trigger passionate arguments about gun control and mental health services; discussion of how to respond to domestic violence often doesn’t even come up.

In reality, it’s impossible to separate domestic violence from gun violence more broadly: 36.7 percent of women living in domestic violence shelters have been threatened or harmed with a gun used by an intimate partner, and in 2011 over half of women murdered with guns in the U.S. were killed by intimate partners or family members.

Mass shootings are terrible tragedies, no matter what contributes to them. And it’s certainly important to consider all the factors that could go into preventing them. The available evidence indicates that one of the first things we should do is start taking domestic violence seriously.