One of two 12-year-old Wisconsin girls accused of nearly stabbing their friend to death to please a mythological demon is not competent to stand trial, a judge ruled Friday.

For weeks the girl's attorneys argued the pre-teen was mentally unstable and needed to be tried in juvenile court, the Associated Press reported. In Wisconsin, defendants age 10 and older who commit severe crimes are tried as adults.

The judge ordered the girl, Morgan Geyser, be committed to Wisconsin's department of health services for treatment, Reuters reported.

The decision comes after the testimony of psychologist Brooke Lundbohm, who evaluated Geyser following her and Anissa Weier's arrest for viciously stabbing their 12-year-old friend 19 times in a wooded park in late May. The victim, whose name has not been released, is at home recovering.

Both girls told authorities they wanted to kill their friend to gain favor and run away with the Slender Man, a tall, faceless being with supernatural powers that was created on the Internet.

Lundbohm testified that Geyser said she sees unicorns, has the power of mind control and that Voldemort, the infamous evil wizard from the "Harry Potter" series, gave her directions, Reuters reported.

Geyser also believes the Slender Man is real, according to the psychologist.

"She does have concern about angering Slender Man and so she has to be careful about what she says," Lundbohm said according to Reuters.

"She presently lacks substantial mental capacity to rationally and factually understand her charge and be a meaningful assistance in her defense."

Geyser could eventually become competent to aid in her defense depending on her treatment, Lundbohm said.

For Weier, the judge set a probable cause hearing date for Sept. 17 and 18. An update on Geyser's progress has been set for Nov. 12, according to Reuters.

Both girls face up to 60 years in prison if they are convicted as adults.