"BEWARE THE SLENDERMAN," A CHILLING LOOK AT THE INFAMOUS CASE OF TWO 12-YEAR-OLD WISCONSIN GIRLS WHO STABBED THEIR BEST FRIEND TO PAY TRIBUTE TO THE FICTIONAL INTERNET LEGEND SLENDERMAN, DEBUTS JAN. 23 ON HBO

The news horrified the world: Two 12-year-old American girls lured a friend into the Wisconsin woods and stabbed her 19 times in an effort to appease a faceless mythical entity known online as Slenderman. But there's more to the story than the dark headlines it generated.

Delving deep into this shocking crime, the sobering documentary BEWARE THE SLENDERMAN examines how an urban myth could take root in impressionable young minds, leading to an unspeakable act, when it debuts MONDAY, JAN. 23 (10:00 p.m.-midnight ET/PT) on HBO.

The documentary will also be available on HBO NOW, HBO GO, HBO On Demand and affiliate portals.

Directed by Irene Taylor Brodsky (HBO's Oscar(R)-nominated "The Final Inch"), BEWARE THE SLENDERMAN covers all sides of this unusual ongoing case, drawing on an eerie array of Slenderman-inspired art, games and self-produced video, all culled from the Internet, along with heart-wrenching, unprecedented access to the two girls' families, courtroom testimony and interrogation-room footage.

On May 31, 2014, in Waukesha, Wisconsin, a 911 call reported a chilling crime. A girl had been stabbed and was found by the side of the road near the woods. The national news media quickly picked up on the story: Victim Payton ("Bella") Leutner had been brutally stabbed and left for dead. The suspects were her friends Morgan Geyser and Anissa Weier. All three were 12 years old.

In separate interrogation rooms, Morgan and Anissa both explained to detectives that they were compelled to kill their friend in order to become proxies of Slenderman, a fictional Internet character they believed was real.

Bella recovered from her injuries, and Morgan and Anissa were charged with attempted first-degree murder. By Wisconsin law, they would be tried as adults, though their lawyers appealed to have the case moved to juvenile court. While the girls awaited the judge's ruling in a juvenile detention center, their baffled parents struggled to understand what happened.

Morgan and Anissa discovered Slenderman on the Internet and came to believe he would hurt their families unless they killed Bella to appease him. Usually depicted as a tall man in a black suit with a featureless white face, Slenderman first appeared on the Internet as part of a 2009 Photoshop contest, lurking behind children in two black-and-white photos. Seen as both a malevolent figure and a guardian angel, Slenderman soon spread to all platforms of the Internet, spawning fan fiction, artwork, games and videos around the world.

Eventually, conspiracy theories about the origins of Slenderman multiplied, and he became a viral meme, with a historic mythology. His character tapped into universal fears, with roots going back to stories by The Brothers Grimm and legends like The Pied Piper of Hamelin.

Anissa and Morgan were particularly susceptible to believing in Slenderman, in part because of their isolation. Anissa's teacher, Tom Haynes, says she was a social outlier who often cried because she didn't have friends. Without a peer group of other girls, the pair became more and more obsessed.

Critically, experts testified during a hearing that Anissa has characteristics of a delusional disorder (the inability to distinguish real from not real). This diminished ability can be found in many people to varying degrees. Psychologist Dr. Michael Caldwell, Psy.D. states, "Adults may have simply eccentric religious or spiritual beliefs or conspiratorial beliefs or things like that, and live out their life with no problems at all."

Additionally, psychiatrists diagnosed Morgan with early childhood schizophrenia, a mental illness also afflicting Morgan's father. Morgan's mother comments that she knew one of their children might also develop schizophrenia, and admits there were signs with Morgan. Yet she never imagined something like this could happen.

A year later, citing the premeditated nature of the crime, the judge ruled the girls were to be tried as adults. Having spent more than two years incarcerated and with their trial date still pending, Morgan and Anissa's saga has now become part of the Slenderman Internet myth.

BEWARE THE SLENDERMAN features interviews with experts who help put the girls' mental state and the Slenderman myth in context, including: digital folklorist Trevor J. Blank, Ph.D.; Brad Kim, editor-in-chief, KnowYourMeme.com; evolutionary biologist Richard Dawkins, Ph.D.; literary critic Jack Zipes, Ph.D.; neurodevelopmental psychologist Abigail Baird, Ph.D.; and psychologist Jacqueline Woolley, Ph.D.

Ultimately, the film reveals how adolescent isolation, mental health issues and the nebulous reality of the Internet created a chilling mandate for two young girls, with life-altering consequences.

BEWARE THE SLENDERMAN was directed and produced by Irene Taylor Brodsky; produced by Sophie Harris; director of photography, Nick Midwig; edited by Gladys Mae Murphy; original score, Benoit Charest. For HBO: senior producer, Sara Bernstein; executive producer, Sheila Nevins.