All the warning signs were there.

Nikolas Cruz bragged about shooting animals, owned an AR-15 rifle and reportedly got expelled from high school after fighting with his ex-girlfriend’s new boyfriend. And then, according to police, he opened fire on students and teachers at the South Florida school Wednesday, killing at least 17 people.

But the warning sign we must all memorize is this: The 19-year-old was abusive toward his ex-girlfriend and so taken with a girl that he essentially stalked her, according to students and teachers at Marjory Stoneman Douglas High School.

Mass shooting in the United States are carried out, overwhelmingly, by men with a history of domestic violence. Fifty-four percent of mass shootings in the United States involve a former or current partner or a family member being killed, according to Everytown for Gun Safety.

Domestic violence and gun violence are both public-health issues that must be taken far more seriously than they are. Our lives depend on it.