That's the question at the heart of "Beware the Slenderman," the forthcoming HBO documentary, for which the first trailer was revealed Thursday.
Morgan Geyser and Anissa Weier are suspected of luring a close friend into the woods in 2014, stabbing her and leaving her for dead, all in pursuit of an Internet boogeyman named Slenderman.
The legend of Slenderman was born online in 2009 with two Photoshopped images depicting children with a tall, faceless, blurry figure in the background. Soon the Internet was caught up in creating a spooky back story for the creature, one that spawned "found footage" on YouTube and even a video game titled "Slender."
"Imagine a modern-day Grimm's Fairy Tale; a Pied Piper for millennials whose myth permeates discussion forums and video games," director Irene Taylor Brodsky said in a statement about the documentary. "Two little girls in Wisconsin are so enthralled and enchanted by this online character, they will kill their best friend for him."
The first trailer for the film leans heavily on the horror tropes that inspired the horrific crime,exploring the blurry lines between fantasy and savagery and what happens to children who can't tell the difference.
"Beware the Slenderman" premieres Jan. 23 on HBO.