WAUKESHA -- Attorneys presented opening statements Tuesday morning in the trial of 15-year old Anissa Weier.
Weier is one of two suspects in the May 2014 stabbing case often referred to as the "Slender Man stabbing."
According to prosecutors, Weier and her friend Morgan Geyser stabbed a classmate 19 times and left her in a Waukesha park.
The girls told investigators they were trying to please the fictional horror character Slender Man.
Weier's attorney, Joseph Smith, said at the time of the stabbing she was a lonely 12-year old struggling with her parents' recent divorce.
Smith said Weier had few friends, and that she and Geyser believed they had to attack their classmate to prevent Slender Man from bringing horror to their families.
"The two believed the only way they could prevent that was to become proxies of the Slender Man," Smith said.
"The evidence will show that, at the time this occurred, Anissa's broken mind caused her to lose touch with reality," Smith said.
Smith said the two girls attacked the victim, then planned to march North to Slender Man's mythical mansion in Northern Wisconsin.
Weier and Geyser were both charged with attempted first degree intentional homicide.
Last month, Weier pleaded guilty to a lesser charge. The state recommended a 10-year prison sentence, although the judge can sentence her to up to 25 years.
As a result of Weier's guilty plea, the jury in her trial will not have to determine if she participated in the stabbing. Instead, the 16 jurors - the standard 12 plus four alternates - will be tasked with determining if Weier is mentally ill.
The burden of proof rests with Weier's attorney to prove that her client is mentally ill, and therefore not legally responsible for the stabbing.
But according to prosecutors, this crime wasn't the result of mental illness.
Assistant District Attorney Kevin Osborne said the state disagrees with the defense's assertion that Weier is mentally ill. He said she carried out the stabbing not out of fear, but to preserve her friendship with Geyser.
"The state believes the defense's conclusions are flawed. They're flawed because they're based on a misunderstanding of what happened here," Osborne said.
"I'm a real person. If I told them they could be my proxies if they killed someone, does that make it alright? No," Osborne said.
Osborne also said Weier told investigators she didn't believe her family was threatened by Slender Man until Geyser informed her of that possibility after the two girls had already carried out the stabbing.
If the jury's verdict comes back in the defense's favor, Weier is facing at least three years in a mental hospital instead of the sentencing options agreed upon as part of her plea deal.
Jurors will be sequestered for the duration of the case. The judge has blocked off up to two weeks for the trial proceedings.
Geyser is expected to go on trial next month.
