In 2009, Eric Knudsen, under the username Victor Surge, created the internet's bogeyman on Something Awful's forums. Slenderman (A.K.A. Slender Man) has since went viral—haunting the 21st century's children in fictional stories posted most prominently on the Creepy Pasta website.

Depicted as a tall, thin, faceless man in a black suit with white skin, Slenderman traumatizes almost always children, stalking them in the back of edited vintage photographs.

Read more: Next American Horror Story season rumored to focus on Slenderman

Five years later, in 2014, two 12-year-old girls in Wisconsin made headlines for taking their obsession with Slenderman to the extreme—stabbing their friend in the woods almost to death as a sacrifice to the fictional character. The victim managed to crawl out of the woods to get help, and later the two girls would openly admit their crime to law enforcement.

[via NME]

HBO soon after announced a documentary based off of Slenderman and the stabbing—Beware The Slenderman, which saw its debut at SXSW in March and will officially air on the channel Jan. 23. The first trailer of the disturbing story has now been revealed. Watch it below, and be sure to let us know what you think in the comments.

Read more: Slenderman documentary—based on the true story—coming soon

The synopsis is as follows:

Shot over 18 months with heartbreaking access to the families of the would-be murderers, the film plunges deep down the rabbit hole of their crime, a Boogeyman and our society’s most impressionable consumers of media. The entrance to the internet can quickly lead us to its dark basement, within just a matter of clicks. How much do we hold children responsible for what they find there?

And the movie poster:

And the trailer: