People gather for a vigil a day after a mass shooting in El Paso. Reuters

Many of the deadliest mass-shooting perpetrators have a history of threatening, committing, or verbalizing domestic violence.

Perpetrators of domestic violence are supposed to be barred from buying guns nationwide.

High-capacity firearms have been relatively easy for recent killers to get their hands on.

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On Monday morning, President Donald Trump made his first public remarks after two mass shootings in El Paso, Texas, and Dayton, Ohio. "Mental illness and hatred pulls the trigger - not the gun," Trump said, arguing that the US must reform mental health laws.

Trump also suggested that mental illness is to blame for the killings that happened at the First Baptist Church of Sutherland Springs in Texas in November 2017.

But scientists say the real problem is that violent, impulsive, and angry men are getting their hands on guns.

Many of the shooters behind the deadliest mass shootings in modern America (listed below) committed violence against women, threatened violence against women, or disparaged women.

Shayanne Gal/Business Insider

According to the nonprofit Everytown for Gun Safety, the majority of mass shootings in the US are in some way related to domestic or family violence. A 2018 Everytown report indicates that in at least 54% of mass shootings, the perpetrator also shot a current or former intimate partner or family member.

A former classmate of Connor Betts, the shooter behind the Dayton, Ohio, shooting told CNN that Betts kept a "rape list" for girls and a "kill list" for boys. Another former classmate said Betts would talk about violence and use harsh language about women. On Sunday, Betts shot his own sister dead.

Perpetrators of domestic violence are legally barred from buying guns, according to federal law. But many have been able to get high-capacity firearms anyway.

The shooter in the Texas church, 26-year-old Devin Patrick Kelley, was kicked out of the Air Force for "bad conduct" years ago. That conduct included assaulting his wife and her child.

The Air Force never reported those details to the FBI, even though the Pentagon requires convicts like Kelley to be added to a federal database for gun-background checks. Kelley also sent threatening text messages to his mother-in-law, who attended the church where the shooting happened on Sunday.

Many mass shooters in recent history had a history of violence against women

Forensic psychiatrist Liza Gold, who teaches psychiatry at Georgetown and edited the book "Gun Violence and Mental Illness," previously told Business Insider that mass shooters tend to be "impulsive and angry about a lot of different things" and many have a history with law enforcement or violence, especially domestic violence.

A 2017 report from the Department of Homeland Security on "mass attacks" in public spaces found similarly that "almost half" of the attackers studied that year were motivated by personal grievances, retaliating for various perceived slights, including being bullied, disliked, or wronged by peers or family members. It's a phenomenon that other researchers have noticed, too.

"Most mass murders are planned well in advance of the outburst, usually as acts of revenge or retribution for perceived slights and wrongs," psychiatrist Michael Stone noted in a 2015 report on "mass murder, mental illness, and men."

Betts and Kelley are just two examples. Omar Mateen, the man who carried out the Orlando shooting at the Pulse Nightclub, reportedly beat his wife and called her the Afghan word for "slut." And both the shooters in San Bernardino and the recent Las Vegas killings at Mandalay Bay had stalked or abused women.

The mass shooting in Sandy Hook, Connecticut, was committed by a man who'd threatened to kill his mother years before he gunned her and 26 other people down at an elementary school. Another mass shooting took place in Killeen, Texas, in 1991, when a man drove his pickup truck though the front window at Luby's Cafeteria shouting, "All women of Killeen and Belton are vipers!"

The one exception on the above list of the deadliest mass shootings is last weekend's El Paso shooting at a Walmart. It's being investigated as a hate crime and act of domestic terrorism fueled by racist, anti-immigrant sentiments.

The US government long barred scientists at the CDC from researching gun violence (in 2018, Congress said the US government could fund research into gun violence, as long as it did not promote gun control). But a now decades-long trend is clear: Violent, armed perpetrators of domestic violence are a deadly force in America.

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