Many mass shooters have a history of domestic violence. It's time to pay attention.

At least five people were killed and 45 people were injured during and after a shooting Friday at the airport in Fort Lauderdale, Florida.

Police have identified the suspect as Esteban Santiago, a 26-year-old National Guard veteran. He most recently lived in Anchorage, Alaska — where, the Alaska Dispatch News reports, he was charged with domestic violence in January 2016.

Santiago’s girlfriend told police that he had bashed in her bathroom door and tried to strangle her. He was later accused of violating his conditions of release on the January charges; police checking up on him found him at the girlfriend's house although he had been ordered to stay away.

The Associated Press also reports that Santiago may have had psychological issues; he told the FBI in November that the government was controlling his mind and forced him to watch ISIS videos. But while it’s common to blame mental illness in the wake of a mass shooting, it’s incredibly misguided, as Vox’s German Lopez has explained. Mental illness just isn’t a good predictor of who will perpetrate violent behavior.

But one of the best predictors of future violent behavior, researchers say, is past violent behavior. And a crucial warning sign — one too often ignored — is domestic violence against intimate partners and other family members.

Not all mass shooters have a previous history of domestic violence, or of violent and erratic behavior bad enough to worry family members — but many of them do. Furthermore, most "mass shootings" aren't how we imagine them; they’re not school shootings or other public massacres. They’re relatively private acts of horror, preceded by red flag after red flag of abusive and violent behavior.

Many high-profile mass shooters are also domestic abusers, and most “mass shootings” are actually domestic violence incidents

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The connection between mass shooters and allegations of domestic violence is nothing new. After Omar Mateen was identified as the perpetrator of the worst mass shooting and most deadly anti-LGBTQ hate crime in modern US history at the Pulse nightclub in Orlando, Florida, his ex-wife told the media that Mateen had violently abused her during their brief marriage in 2009.

There was Robert Lewis Dear, the alleged 2015 Planned Parenthood shooter in Colorado Springs, who was charged with sexually assaulting a woman at knifepoint in 1992, was accused of domestic violence by his then-wife in 1997, and had an order of protection obtained against him by a neighbor in 2002 for stalking and “unwanted advancements.”

There was John Houser, who killed two and injured nine in a movie theater in Lafayette, Louisiana, in 2015, and whose wife and daughter filed an order of protection against him for domestic violence in 2008.

There was James Huberty, who killed 21 people at a California McDonald’s in 1984 and whose wife reported him to police for giving her a "messed up" jaw. The list goes on.

Mass shootings are so scary because they’re so unpredictable. They can happen anywhere and to anyone, and they are often carried out by people without criminal histories that could have prevented them from buying a gun in the first place.

But in fact, most "mass shootings" are all too predictable. And their victims are the women and children who are entangled in the lives of violently abusive men.

More than half of mass shootings (defined as a shooting in which at least four people are killed with a gun) involve a current or former intimate partner or a family member. Most of the victims of those shootings, 81 percent, are women or children. And 70 percent of all mass shootings happen inside the home, not out in public. These shootings make the local news, but they are both so private and so sadly routine that they almost never get the massive national attention that rarer public shootings do.

"Men who commit violence rehearse and perfect it against their families first," wrote Pamela Shifman and Salamishah Tillet in a New York Times op-ed in February. "Women and children are target practice, and the home is the training ground for these men’s later actions."

Domestic violence is a screaming red flag for future violent behavior, but keeping guns away from abusers isn’t always easy

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"We know that violence is the best predictor of future violence," said Shannon Frattaroli, an associate professor at the Johns Hopkins Bloomberg School of Public Health who researches the connection between gun violence and domestic violence. "If someone has demonstrated past violent behavior, it's probably the best indicator we have of the risk of being violent in the future."

Domestic violence in particular is extremely predictable. It’s common for police to be called multiple times, sometimes dozens, for domestic violence incidents before a victim is ultimately murdered by her abuser. Recidivism rates for domestic abusers are high. And a substantial body of research shows that victims of domestic violence, particularly women, are put at much greater risk of being murdered when a gun is involved.

So if we care about protecting victims, there’s already a lot of incentive to get guns out of the hands of domestic abusers. And indeed, there are already some laws in place to do this. Federal law prohibits the sale or possession of guns for anyone convicted of a domestic violence misdemeanor, or anyone who is subject to a domestic violence restraining order. Some states have laws that allow or require law enforcement agents to seize any guns found at the scene of a domestic violence incident.

But not all states have the same laws, and federal law has significant limitations. Non-married partners who don’t live together are not protected, nor are family members other than children. It helps that federal law covers misdemeanors and restraining orders, since it’s difficult to get a felony conviction for domestic violence. But federal law only covers a full restraining order — and victims face the highest risk for violent retaliation from their abusers after an initial temporary restraining order is granted, and that comes before a full order.

Implementation is also a huge barrier to taking guns away from domestic abusers, Frattaroli said. It takes a lot of action from law enforcement to actually take away someone’s gun after he has been served with a domestic violence restraining order.

First, police officers have to know that an abuser owns a gun in the first place — and data on that can be spotty because not every state has a gun registry or gun sale database, and not all of those databases are complete. Then an order has to be served, which requires actually finding the offender. And then law enforcement actually has to go about seizing the firearm.

“There are some places that are doing some great work to implement and enforce these laws,” Frattaroli said. “But my sense is it's not routine, it's not commonplace, it's not what is happening across the country on a systematic scale.”

Plus, for new gun purchases, background checks still aren’t universal. So it’s very possible for someone who is subject to a domestic violence restraining order — temporary or otherwise — to get a gun even if he isn’t legally supposed to.

What might good policy solutions to this problem look like?

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Frattaroli and her colleague April Zeoli laid out a list of policy recommendations in the book Reducing Gun Violence in America.

One key recommendation is universal background checks — another major proposal that congressional Democrats have been pushing in their filibusters and protests. This would help solve the implementation problems mentioned above.

To further beef up implementation efforts, Zeoli and Frattaroli recommend establishing a federal training program to help state and local law enforcement agencies do a better job of enforcing the laws that already exist. They also say we should give states incentives to create gun registries, and to automatically update their background check systems as new domestic violence restraining orders and misdemeanor convictions come in.

Perhaps the most intriguing suggestion Frattaroli mentioned, though, is something called a gun violence restraining order. California became the first state to pass a law like this in 2014.

Much like a domestic violence restraining order, a gun violence restraining order gives a concrete, emergency legal step for victims or concerned family members to take if they know that someone close to them is dangerous. They can petition the court to prohibit the person from buying or possessing a gun for a defined period of time — a year, for instance.

The basic idea behind this policy is that family members and friends of an abuser, as well as law enforcement officers who answer their distress calls, are on the front lines of abuse. They are the most likely to know if a person has a pattern of violent behavior, and they are most likely to suffer from it. Yet unless someone has committed a crime or can be involuntarily committed to a mental institution, there’s not much anyone can legally do to keep guns out of his hands.

Omar Mateen was known to have a violent temper by more than one person in his life. The parents of Jared Loughner, who shot Rep. Gabrielle Giffords and killed 10 people in Tucson, Arizona, in 2011, knew he was violent and took away his shotgun but couldn’t do anything more unless he had committed a crime or unless they had decided to try to have him involuntarily committed to a mental institution. The family of Elliot Rodger, who went on a misogynistic killing spree in Santa Barbara, California, in 2014, was similarly worried about his threatening behaviors and similarly powerless to do much about it.

We can’t predict who will become a mass shooter, nor can we save every potential victim of domestic violence. But it would be an unforced error not to do all we can to keep guns out of the hands of people who are known to be violent — and it’s a lot easier to predict violent behavior in general than the specific decision to commit a mass shooting.