Why So Many Mass Shooters Have Domestic Violence in Their Past

James T. Hodgkinson, who injured Rep. Steve Scalise (R-LA) and several others when he opened fire on Republican members of Congress and aides at a baseball practice Wednesday morning, had at least one thing in common with many other mass shooters: an alleged history of violence against women.

Eleven years before he stepped up to that Alexandria baseball field, Hodgkinson was arrested for domestic battery and discharge of a firearm after he allegedly punched his daughter’s friend and shot at the friend’s boyfriend, according to a 2006 police report reviewed by TIME. The police report also describes him throwing his daughter “around the bedroom,” and “hitting her arms, pulling hair.” Once the daughter got into her car to attempt to flee, the police report says Hodgkinson was “choking” her “while she was holding onto the steering wheel” and he attempted to cut her seat belt. The charges were ultimately dismissed.

Hodgkinson, who was killed by police in Wednesday’s shooting, is the latest in a line of shooters who have a history of alleged family violence. According to a comprehensive analysis by Everytown for Gun Safety, which advocates for tighter restrictions on guns, 54% of mass shootings between 2009 and 2016 were directly related to domestic or family violence — meaning that a current partner or family member is one of the victims. In one of those cases, Cedric Anderson walked into his new wife’s elementary school classroom in San Bernandino, Calif. in April and killed her, an 8-year old special needs student, and himself.

But even among the other 46% of mass shootings that don’t directly involve an intimate partner, many of the attackers have a violent misogynistic incident in their past. The Everytown study found that 42% of all mass shooters had exhibited at least one warning sign, such as a prior violent act or domestic violence incident.

Omar Mateen, who killed 49 people and injured 53 others in the Pulse nightclub massacre in Orlando last June, had an abusive relationship with his ex-wife, who said he frequently beat her, pulled her hair and dug his fingernails into her wrists. Robert Lewis Dear, who killed three people and wounded nine others when he opened fire on a Planned Parenthood in Colorado Springs in 2015, had been accused of domestic violence by two of his ex-wives and had been arrested for rape in 1992. Elliot Rodger drafted a manifesto describing how he “burned with hatred for all women who rejected me through the years” before he went on a shooting rampage in Isla Vista, Calif. in 2014, killing six people and targeting a sorority at UC Santa Barbara. Less than two hours before Cedric Ford began randomly shooting people in the Kansas lawnmower factory where he worked in 2016, he received a court order to stay away from a woman he had been living with.

Experts say there is no comprehensive research on the shared characteristics of mass shooters. But some who have studied the people who commit mass attacks in the U.S. see a linkage in the propensity for violence. “It’s related to this idea of toxic masculinity,” says April Zeoli, an associate professor at the School of Criminal Justice at Michigan State University who studies domestic violence, homicide and firearms. “Domestic violence can be a harbinger of greater violence to come.”

Zeoli says domestic violence incidents, while often confined to the home, can be indicators of lethal urges that could be unleashed on the public. “This feeling of entitlement, of acceptability of violence, can erupt in some rare and extreme cases into mass violence,” she says.

But others caution that there is no published evidence to suggest that domestic abusers are more likely to become mass shooters — and the correlation may be entirely coincidental, if it exists at all. “There has been this narrative that’s been created that somehow somewhere these things are linked, and we at this point in time have no evidence for that,” says Susan B. Sorensen, a social policy researcher at the University of Pennsylvania who conducts research on firearms and intimate partner violence. “Domestic abuse is the most common call to law enforcement. And have all those guys gone on to be mass shooters?” According to a 2014 Department of Justice report, 21% of all violent offenses between 2003 and 2012 were related to domestic violence.

In an effort to keep guns out of the hands of domestic abusers, 12 states now have laws requiring anybody served with a domestic violence restraining order to relinquish their guns, and nine states require those convicted of a domestic violence misdemeanor to give up their weapons, according to a 2016 study from the Law Center to Protect Gun Violence. Of those 12, only a handful require police to get proof that the suspect has relinquished the guns.

To Zeoli, cracking down on gun ownership for domestic abusers can prevent these men from escalating from intimate violence to mass violence. “If you are someone who is willing to put your intimate partner through violence and beatings and control,” she says, “then those characteristics also make you someone who may be more willing to commit these fatal shootings.”

Correction: The original version of this story misspelled the name of April Zeoli.