Two 12-year-old girls in Waukesha, Wisconsin, lured their friend into the woods to murder her over 10 years ago. They stabbed Payton Leutner 19 times, according to police, to appease a fictional horror character of online lore named Slenderman.

The crime was shocking because these were suburban girls motivated to kill by basically nothing. A made-up story manifested itself in shocking violence in real life — “IRL,” as the kids used to say. How did obscure internet lore cross the chasm from online to real life?