Waukesha County Circuit Judge Michael Bohren said Weier will be committed to a mental institution.
A Wisconsin teenager who was inspired by mythical character Slender Man to attempt to murder a classmate has escaped a prison sentence after a jury found her to be mentally ill.
Anissa Weier told investigators that she and co-defendant Morgan Geyser believed they had to kill their victim in "dedication" to Slender Man, a fictional horror website character.
Under Wisconsin law, 10 of 12 jurors must agree on whether Weier was mentally ill and if so decide if she was responsible for her actions.
McMahon urged the jury to send her to a mental hospital rather than convict her as a criminal which would have seen her serve over 10 years in prison. McMahon also said that a judge can order up to a 25-year commitment for Weier.
While Weier was dealing with her parents' divorce, teachers began noticing symptoms of depression, he said. "There've been consequences for three years, and it will continue one way or the other".
Weier told authorities she believed Slender Man would harm herself and her family if she didn't stab the victim. At one point before the attack, prosecutors claim Weier unleashed Geyser by saying "go berserk", according to the Journal Sentinel. Her trial is set to begin October 9, Mail Online reports.
A shared delusion and an interest in the paranormal led two girls to stab another 12-year-old girl in a Wisconsin park as a tribute to the fictional horror character Slender Man, a psychologist testified Wednesday.
"At the moment of this bad tragic event, that she was confused and convinced that something real was going on with this very unusual character called Slender Man", he said.
Slender Man first appeared on the internet in 2009.
Three psychologists testified that she suffered a shared delusion that she and Geyser had to kill Leutner to become Slender Man's servants and prevent the character from killing their families.
Doctors said Payton Leutner nearly died in the attack.
Waukesha County Deputy District Attorney Ted Szczupakiewicz told the jury during his closing arguments Friday that the girls had planned the attack for months and that they were not in a "kill or be killed situation".
Both Weier and Geyser were charged with being a party to attempted first-degree intentional homicide.
Weier, now 15, pleaded guilty to attempted second-degree intentional homicide in a deal with prosecutors in August.