Story highlights The 15-year-old will spend at least 3 years in a mental hospital

Two teens were accused of stabbing a classmate in 2014

(CNN) A Wisconsin jury says one of two teens charged in the 2014 Slenderman stabbing of a classmate was mentally ill when the attack happened.

Last month, Anissa Weier, 15, had pleaded guilty to attempted second-degree homicide due to mental illness or defect in the stabbing as part of a plea agreement. A jury trial on her case, which began Monday, was set to determine whether Weier was mentally ill when she committed the crime.

A total of 10 out of 12 jurors agreed on Friday that Weier had a mental disorder when she and her classmate Morgan Geyser stabbed their sixth-grade classmate 19 times. The girls were allegedly trying to please the fictional internet bogeyman Slenderman

The girls, who were 12-years-old at the time, were charged with attempted murder and both have been tried as adults.

Waukesha County Circuit Judge Michael Bohren said Weier will be committed to a mental institution. If the jury had found her guilty, she could have gone to prison for 10 years.

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