When 12 students and one teacher were killed in Littleton, Colo., 20 years ago, it became what at the time was the worst high school shooting in U.S. history. It also marked when American society was first handed a script for a new form of violence in schools.

We make that observation as researchers — a psychologist and a sociologist — who have been studying mass public shootings as part of a grant from the U.S. Department of Justice.

Since the 1999 tragedy at Columbine High School, we identified six mass shootings and 40 active-shooter incidents at elementary, middle or high schools in the United States. Mass shootings are defined by the FBI as an event in which four or more victims died by gunfire.

In 20 — or nearly half — of those 46 school shootings, the perpetrator purposely used Columbine as a model.

The ties that bind to Columbine

In our study of school shootings, we only looked at cases where a gun was fired on campus, following the practice of the Washington Post’s database on school shootings. Had we included foiled plots, the number would be significantly higher.

Several school shooters in our study were fascinated with Columbine and researched the massacre before their own. This includes the Parkland shooter, a 14-year-old who aspired to be “the youngest mass murderer,” and a 15-year-old who shot at his teacher after she refused to praise Marilyn Manson, the rock singer erroneously blamed for inspiring the Columbine killers.

The timing of the April 17 threat to Colorado schools is no coincidence. Prior perpetrators chose the anniversary of Columbine to commit their shootings, including one month and two years after. A different shooter talked of how he was going to “pull a Columbine.” Others discussed Columbine with classmates, even joked about it.

The Sandy Hook Elementary School shooter idolized the Columbine killers and curated a Tumblr account paying homage, alongside a graphic collage of Columbine victims. A North Carolina shooter was so obsessed with Columbine that he took a vacation there with his mother and fantasized about “finishing off” any wounded survivors.

Perpetrators dressed in trench coats like the Columbine shooters, including those responsible for the 2018 Santa Fe shooting, where 10 people died, and a 2004 nonfatal shooting in New York. Indeed, the trench coat has appeared in subsequent school shootings because Columbine gave it meaning beyond any intrinsic use.

Why Columbine?

Before Columbine, there was no script for how school shooters should behave, dress, and speak. Columbine created “common knowledge,” the foundation of coordination in the absence of a standardized playbook. Timing was everything. The massacre was one of the first to take place after the advent of 24-hour cable news and during the “year of the net.” This was the dawn of the digital age of perfect remembering, where words and deeds live online forever. Columbine became the pilot for future episodes of fame-seeking violence.

Separating myth from reality

Our research has found that school shootings have nothing to do with jock envy, satanism, video games, or Keanu Reeves, and school shooters are not psychopathic masterminds. In fact, these sound-bite explanations for aberrant behavior only blind us to the reality of school violence.

School shooters are almost always current students of their schools. They are students who are in crisis, students who have experienced trauma, and students who are actively suicidal prior to the shooting and expect to die in the act. Such children have always existed. But for 20 years they’ve had a new script to follow.

And we, the public, have contributed to the production and direction of this script. Again and again and again. Through our obsession with true crime and films, books, memes, and entire websites devoted to Columbine. By releasing CCTV footage of the shooting to the public. By running our children through regular lockdowns and active-shooter drills starting in preschool through 12th grade. By sending them to school through secure entrances with clear backpacks and bulletproof binders. Society and culture have reared a Columbine generation, modeling that this is just part of childhood in America.

Flipping the script

After 20 years, it’s time to rewrite the script being rehearsed with young people.

It starts with no names, no photos, and no notoriety for mass shooters in media coverage — which is why we don’t indulge here. The next step is a paradigm shift from homeroom security to holistic violence prevention in schools — mental health, supportive environments, strong relationships, and crisis intervention and de-escalation. Teachers should feel as comfortable asking a student about suicide as they feel going into lockdown; empowered to spend as much time teaching empathy and resilience as they do now training to run, hide, fight.

The victims and survivors of school violence must not be forgotten, but to prevent another two decades of contagion and copycats, it requires a recognition that it is time to close the curtain on the spectacle of Columbine.

Jillian Peterson is a professor of criminal justice at Hamline University. James Densley is a professor of criminal justice at Metropolitan State University. They both receive funding from the National Institute of Justice. A version of this piece first appeared on The Conversation.