A 12-year-old Milwaukee girl accused of plotting to kill a friend to curry favour with a fictional internet character shows signs of mental illness and should be in a hospital, her defence attorney said Tuesday.

The girl and another 12-year-old have been charged as adults with first-degree attempted homicide in a stabbing that nearly killed another child the same age. The two girls told investigators they plotted for months to kill their friend because an online character called 'Slender Man' required them to kill someone before they could become his "proxy."

Anthony Cotton, an attorney for one of the girls charged in the stabbing, said her parents called him while she was being questioned at the police station because officers had rejected their request to see her. Police read the girl her rights but were not required to have a parent or lawyer present if she didn't ask for them, he said.

Cotton said he would push to get the girl's case transferred to juvenile court, where more social services and mental health treatment would be available.

"She's 12 and she has mental health issues," Cotton said. "There's no question that she needs to go to the hospital."

Judge disallows move to hospital

The girls are being held at a juvenile detention centre after a court commissioner set bail at $500,000. Cotton said his client's family can't pay that, and a judge already rejected his first motion to move the girl to a hospital. He said he'll seek a mental health evaluation as a first step toward a second request.

The girls told investigators they read about Slender Man on the horror website creepypasta.wikia.com. It's not clear

Slender Man stabbing

The girls spent time at this suburban Milwaukee park before heading to a nearby wooded area and brutally attacking their classmate, stabbing her 19 times and leaving her severely injured. (Carrie Antlfinger/The Associated Press)

whether they got access to the website at home or at school, but a school administrator said employees were reviewing various websites to see if they should be blocked after the stabbing.

According to court documents, the girls told investigators they invited their friend to a sleepover at one of their houses on Friday and planned to duct tape her mouth while she was sleeping, stab her in the neck, put the covers over her to make it look like she was sleeping and run away to Slender Man's mansion.

They backed out of that plan, deciding to kill her on Saturday in a nearby park bathroom so blood would go down the drain. They convinced the girl to go to the park with them and got her into the bathroom. One of the girls handed the knife to the other but she couldn't bring herself to stab the victim, she said. She gave the knife back to the other girl but she couldn't go through with it either, the complaint said.

They went into the woods, where one girl pushed the victim down and sat on her. The girls then traded the knife back and forth between them before one of them finally tackled the victim again and began stabbing her, according to the complaint.

The girls left the victim lying in the woods. She crawled to a road where a bicyclist found her lying on the sidewalk. Police arrived and she gave them the name of one of the girls who attacked her.