Attorneys for one of the two Wisconsin middle schoolers charged with stabbing their classmate  presented a self-defense argument before the court this week. 

Psychologist Deborah Collins testified that Anissa Weier, 13, believed that the horror wiki character Slender Man would hurt her and her family if she did not kill someone. 

Weier and her friend, Morgan Geyser, 12, told Waukesha County police that they believe Slender Man - a fictional character on the Creepypasta wiki - is real, and lured their friend, 12-year-old Payton Leutner, to a sleepover in May 2014 to kill her. 

The girls, who attend Horning Middle School together, went to Skateland Entertainment Center to celebrate Geyser's birthday, then spent the night over at Geyser's house. 

Weier told police that she and Geyser planned to duct tape Leutner's mouth and stab her in the neck that night, but decided to attack her the next day in a park instead.

The next morning, the three girls went to David's Park, and played hide and seek in the woods. After tackling their classmate and pinning her to the ground, one or both of the girls stabbed Leutner 19 times in the legs, arms, and torso.  Remarkably, Leutner survived.

Geyser and Weier were charged as adults with attempted murder, and were found competent to stand trial in December. Judge Michael Bohren will decide next month whether the cases will proceed.