Interrogation footage of Weier (below) and Geyser form the core of HBO’s new documentary
Michael Sears—Pool Milwaukee Journal-Sentinel/AP
January 26, 2017 6:39 AM EST

The crime was grisly. In 2014, Morgan Geyser and Anissa Weier lured a friend into the woods on the edge of Waukesha, Wis., and stabbed her 19 times. All three girls were 12. More disturbing yet was the motive: the pair told police the attack, which their victim survived, was intended to placate a fictional Internet bogeyman known as Slender Man.

The case, which is headed to trial in adult court, is the subject of HBO’s new documentary Beware the Slenderman (Jan. 23). (The girls pleaded not guilty on grounds of mental illness.) Even amid a true-crime renaissance–NPR’s Serial podcast, Making a Murderer on Netflix–Slenderman finds fresh ground. Extensive interrogation footage of Geyser and Weier shows them at turns immature and vulnerable, at others disturbingly detached. And director Irene Taylor Brodsky tries to rise above mere prurience by weaving in issues of mental health and child incarceration. She has sympathy for the two girls. “It was obvious this was a zeitgeist example of how we are adapting” to digital life, she says, while adding that Geyser and Weier “were clearly in a very distressed and disturbing state.”

FROM MEME TO ATTEMPTED MURDER

ORIGIN

Slender Man is usually depicted as a tall, faceless figure who wears a dark suit and has tentacles for arms. He was created in 2009 by Internet user Eric Knudsen, who was participating in an online Photoshop contest.

OLD MYTHS

Slender Man’s victims are often portrayed as being plagued by a “Slender sickness”–paranoia, nosebleeds, and nightmares–before being taken to the woods to be murdered. It’s a new take on an ancient, cross-cultural tradition of bogeymen, fictional characters used to scare kids into behaving. Like “sack men” depicted in India, Latin America and across Eastern Europe, he kidnaps and murders children.

NEW URBAN LEGEND

Slender Man stories proliferated in various online forums, becoming the subject of video games, wiki pages and numerous Slenderblogs. A series of YouTube videos that follow the myth in Blair Witch–style shorts have racked up more than 90 million views.

FIRST CONTACT

Geyser and Weier first learned of Slender Man on CreepyPasta, a horror-story website. The 12-year-olds later told authorities they believed he would hurt their families unless they sacrificed a friend. They begin plotting their attack over the course of several months.

ATTACK AND TRIAL

In June 2014, Geyser and Weier lured a friend into the woods by playing a game of hide-and-seek and stabbed her 19 times. Their victim, also 12 years old, survived. The two girls were charged as adults for attempted first-degree intentional homicide; their trial will take place in Wisconsin.

This appears in the February 06, 2017 issue of TIME.

Contact us at letters@time.com.

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