One of the two girls accused of attempting to stab their 12-year-old friend to death to appease a fictional online character in the US is to plead not guilty on mental health grounds. Morgan Geyser, who was also 12 at the time of the “Slender Man” attack in 2014, is being held in a psychiatric facility after being diagnosed with schizophrenia.

She and co-defendant Anissa Weier appeared at Waukesha County court on Friday, where their legal representatives called for the trial to be moved to another region because of prejudice.

The judge did not grant the request but appointed two psychiatrists to evaluate Geyser’s mental state. Weier pleaded not guilty last year.

The two defendants, now aged 14, are being tried for attempted murder as adults after losing an appeal and face decades in jail if convicted.

Prosecutors say they plotted to kill their classmate for months as a sacrifice to the fictional character “Slender Man” after reading horror stories online.

They played hide and seek in the forest with their friend on 31 October 2014 before launching the attack, where one of the girls allegedly held her friend down while the other stabbed her 19 times.

The victim managed to drag herself out of the forest and was found by a passing cyclist, managing to name her attackers before being taken to hospital.

She underwent emergency surgery and has since recovered and returned to school.

Police found Geyser and Weier walking nearby, with a knife in one of their rucksacks.

Investigators say the girls spoke of their desire to become Slender Man’s “proxies” and sacrifice their friend to demonstrate their loyalty and prevent the figure from hurting their families. Geyser and Weier are next due in court on 13 October.