On April 20th, 1999, two students at Columbine High School murdered twelve students and a teacher and sent the nation scrambling for answers.

As Dave Cullen detailed in his book, Columbine, initial news coverage quickly portrayed the perpetrators as two alienated students, obsessed with carrying out a revenge fantasy against bullies. Those early media profiles have since proved incomplete, but they continue to shape the way we understand school shootings today.

More than a decade after Columbine, we’re still struggling to figure out not only what causes school shootings, but whether or not we’re seeing more of them. Former student John Savage says, “I think it’s important to kind of keep in mind that there are a lot of schools all over the world, where no one has ever been shot.”