A judge in Wisconsin ordered Monday separate trials for two Wisconsin girls charged with attempting to kill their classmate in a bid to appease Slender Man, a fictional horror character. The girls — 14-year-old Morgan Geyser and 15-year-old Anissa Weier — have been charged as adults and they have pleaded not guilty.

Waukesha County Circuit Judge Michael Bohren ordered separate trials for Geyser and Weier after both defense teams and prosecutors agreed that a joint trial is likely to pose legal risks.

In May 2014, the girls invited classmate Payton Leutner for a sleepover. They all were 12 at the time. According to reports, Weier and Geyser lured Leutner into the woods and stabbed her 19 times, after having planned it all for months to “impress” Slender Man. The popular fictional character is also reported to have become the subject of a game.

A bicyclist saw Leutner who crawled out of the woods the following the incident. She was hospitalized for six days.

A judge previously ruled both Weier and Geyser were competent enough to stand trial. Weier was reportedly diagnosed with a delusional disorder that made her believe Slender Man actually existed. A health expert also testified that Geyser suffered from schizophrenia but did not take medication for the mental disorder. Both the girls cited their mental problems in their not guilty pleas.