MADISON, Wis. - The defense attorney for a Wisconsin girl accused of helping stab a classmate to please the fictional horror character Slender Man says she was under the "command and control" of a delusional disorder.

That argument was a part of opening statements in the mental competency trial of 15-year-old Anissa Weier, accused of ordering a friend to stab a classmate multiple times to curry favor with the character.

Attorney Joseph Smith told jurors Tuesday that Weier's "broken mind" caused her to lose touch with reality and participate in the stabbing of Payton Leutner at a Waukesha park in 2014. The defense contends Weier is not guilty because she was mentally ill. If jurors agree, Weier would be sent to a mental health facility instead of prison.

Assistant District Attorney Kevin Osborne said Weier and co-defendant Morgan Geyser knew what they were doing was wrong. Osborne says the initial plan was for Weier to stab Leutner, but she couldn't do it and instead commanded Geyser to do the stabbing.

The girls were 12 at the time.

Twelve jurors and four alternates were selected Monday to hear the case.