HBO has released the official trailer for "Beware the Slenderman."
The documentary is based on the true story of two 12-year-old Waukesha girls accused of stabbing their classmate Payton Leutner 19 times to please the fictional horror character Slender Man.
Leutner survived the attack.
The two girls, Anissa Weier and Morgan Geyser, were both tried for attempted homicide charges in adult court. Both pleaded not guilty by reason of mental disease.
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"Beware the Slenderman" premieres January 23 on HBO.
