Police in Madison, Wisconsin, are searching for Morgan Geyser after she left a group home where she had been living under court ordered supervision.
Officers said she removed her monitoring bracelet and was last seen on Saturday evening in a west side residential area with an adult acquaintance.
Geyser is 23 and was one of two girls convicted in the 2014 stabbing of their sixth grade classmate in an attempt to impress the fictional internet figure known as Slender Man.
The crime shocked the country and raised questions about the influence of online mythology on young adolescents.
The attack took place in Waukesha when Geyser and her friend Anissa Weier, both 12 at the time, lured their classmate Peyton Leutner into a park. Leutner was stabbed 19 times and left in the woods but managed to crawl to a bike path where a passing cyclist found her alive.
Leutner later said the trio had been close friends. She told ABC that Geyser often spoke obsessively about Slender Man and that she had found the character frightening. She had gone to Geyser’s home that night for a sleepover to celebrate Geyser’s birthday.
Geyser pleaded guilty at 15 to attempted first degree murder and was committed to a mental health institution instead of being given a prison sentence. During her sentencing hearing in 2018 she apologised to Leutner and her family and said she had never intended for the events to unfold as they did.
A judge approved her conditional release from the Winnebago Mental Health Institute in January and she had been living in supervised housing. Her lawyer Tony Cotton urged her on Sunday to turn herself in and said they had worked too hard to secure her freedom for her to throw it away.
Cotton said it was not clear how she left the group home or who may have helped her. Police confirmed that she had been living in a Madison facility on the same street where she was last seen.
Weier pleaded guilty to attempted second degree homicide due to mental illness and was committed for 25 years. She was released in 2021 on conditions that include living with her father and wearing a GPS tracker.
