Morgan Geyser, who stabbed a classmate to please the internet horror character Slender Man, is missing after cutting off her monitoring bracelet.
Now an adult, she was sentenced to 40 years in a psychiatric hospital after carrying out the nearly fatal attack in 2014.
However police in Madison, Wisconsin, said on Sunday that she was at large and her whereabouts were unknown.
“If you see Geyser, please call 911,” the force said.
She was last seen around 8pm local time on Saturday with an adult acquaintance.
Geyser had been moved to a group home this year after being granted conditional release from the Winnebago Mental Health Institute.
Her lawyer Tony Cotton said he did not know what had happened and urged Geyser to turn herself in.
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“It’s in her best interest for her to turn herself in immediately and not continue with this course of action,” he said in an Instagram video post.
“We don’t know any of the facts about what happened or who might have assisted her.”
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Geyser and her friend, Anissa Weier, were 12 years old when they lured a classmate to a suburban Milwaukee park after a sleepover, authorities said.
Geyser stabbed their victim more than a dozen times as Weier egged her on. The victim barely survived the ordeal.
The girls told investigators that they had carried out the horror attack in order to please Slender Man, an online horror character.
They said they wanted to earn the right to be Slender Man’s servants and they feared he’d harm their families if they didn’t follow through.
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Created in 2009, Slender Man is depicted as a mysterious figure with long limbs that is photo-edited into everyday pictures.
He grew into a popular bogeyman and has appeared in games, online stories and a 2018 film.
Geyser pleaded guilty to attempted first-degree intentional homicide in a deal with prosecutors to avoid prison.
Weier pleaded guilty to attempted second-degree intentional homicide. She was also sent to the psychiatric centre and was granted release in 2021.
