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

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

Hodgkin son, whose attack injured House Majority Whip Steve Scalise, a congressional aide, a lobbyist and two Capitol Police officers, frequently criticized President Donald Trump and other GOP leaders on social media and in letters to his local newspaper and 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 of 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 soft There is one thing, though, that an alarming number of the recent mass shooters in the United States 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, Calif., 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 failed to smile at him. Ismaaiyl Brinsley, who murdered two police officers in Brooklyn, N.Y., in 2015, shot his ex-girlfriend in the stomach just hours earlier.

Cedric Ford, who shot 17 people last year at the Newton, Kan., plant where he worked, killing three, had been accused of abusing his ex-girlfriend and had been 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 and harassment toward women.

And Omar Mateen, who murdered 49 people at Pulse nightclub in Orlando, physically abused his wife for years.

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. A police narrative on file with the St. Clair County, Illinois, Sheriff's Department says 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. 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. Other research has found that those who abuse their domestic partners are also more likely to abuse children and animals, and that 68 percent of men in a sample of batterers exhibited other "problem behaviors," such as fights, previous arrests or drunken driving.

Of course, it shouldn't be a surprise domestic violence and mass shootings are correlated. As I have pointed out before, domestic violence is a form of violence, just one that we don't always taken as seriously as other kinds. People who are likely to act violently often start with those nearest to them, who are vulnerable due to proximity, and who are often financially, emotionally or legally dependent on their abuser.

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. Amass 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 more than half of women murdered with guns in the United States 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.

Nancy Leong is an associate professor at the University of Denver Sturm College of Law.