Teen Who Urged Friend to Stab Girl for 'Slender Man' Found Mentally Ill, Family 'Deeply Disappointed'

She will stay in a mental facility for at least three years.

A Wisconsin girl, who played a role in the 2014 stabbing of her classmate to reportedly please a fictional character, will not serve prison time after she was found to be mentally ill.

Anissa Weier, 15, was found not to be criminally responsible for the vicious stabbing of Payton Leutner and will reside in a hospital for treatment in lieu of time behind bars, WISN reported.

Read: Slender Man Stabbing: 2 12 Year Olds Accused of Stabbing Friend to Please Mythical Entity

Leutner was lured to a park in Waukesha, a Milwaukee suburb, on May 31, 2014, by Weier and another classmate, Morgan Geyser. Geyser stabbed Leutner 19 times while Weier reportedly urged her on, authorities said. 

Both Weier and Geyser told police they felt they had to kill Leutner to become Slender Man’s servants. As followers of the character, they believed their families would be protected from the demon’s wrath, according to reports. 

A passing bicyclist found Leutner, who was clinging to life. All three girls were 12 at the time.

Both girls were charged with attempted first-degree intentional homicide and initially pleaded not guilty by reason of mental illness or defect, reports said. 

Weier, now 15, pleaded guilty to attempted second-degree intentional homicide in a deal with prosecutors in August, according to reports. The teen claims she was mentally ill during the attack and not responsible for her actions, in a bid to be sent to a mental institution rather than prison, The Associated Press reported.

A plea agreement before trial called for her to spend at least three years in a mental hospital if judged mentally ill, and 10 years in prison if not, according to the report. 

On Tuesday, before the Waukesha County court’s verdict, Weier's attorney, Joseph Smith reportedly said that the divorce of the teen’s parents caused her to be severely depressed and that she latched on to Geyser. 

“Anissa’s broken mind caused her to lose touch with reality,” Smith told The AP. “Anissa was under the command and control of a delusional disorder.”

Prosecutors argued that the attempted murder was calculated and that the girls knew what they were doing was wrong, reports said. 

Read: Teen in 'Slender Man' Stabbing Attack Pleads Guilty to Lesser Charge: 'I Just Wanted It to Be Over'

On Friday, 10 of 12 jurors, the minimum required by law, voted Weier mentally ill, The AP reported. The same number, though not the same jurors, also voted that she was not criminally responsible for her actions, according to reports.

Leutner’s family called the verdict "deeply disappointing."

The jury's decision "forces our family to relive this horrific crime every six months wondering if (Weier and Geyser) will be released," relatives said in a statement released by WISN.

Geyser has pleaded not guilty to one count of attempted first-degree intentional homicide by reason of mental disease or defect, reports said. Her trial is set to begin Oct. 9.

Watch: Could Murder Be a Side Effect of Taking Too Much Cold Medicine?