Two 12-year-old Wisconsin girls accused of stabbing their friend nearly to death in the woods to please a fictional character struggled to decide who should actually do the deed and expressed at least some regret to detectives, according to court documents.

The girls, both from Waukesha, a Milwaukee suburb, told investigators they had been planning to kill their 12-year-old friend for months to please Slender Man, a fictional demon-like creature they learned about through a horror website, according to a criminal complaint. They invited the girl 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, the complaint said.

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.

One girl told a detective she understood they were going to end a life and she regretted it.

"The bad part of me wanted her to die, the good part of me wanted her to live," the girl told the investigator.

The other girl told detectives they both stabbed the victim. At one point that girl said she was sorry and what she did was "probably wrong."

Charged as adults

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.

Both girls were charged as adults with first-degree attempted homicide Monday in Waukesha County Circuit Court; they each face up to 60 years in prison if convicted. A court commissioner set bail at $500,000 cash per child.

"I recognize their young ages but it's still unbelievable," Court Commissioner Thomas Pieper said during one of the girls' initial court appearances Monday.

The victim suffered 19 stab wounds; one missed a major artery near her heart by a millimetre, doctors told police. She was in stable condition Monday. The court documents did not name her.

The Associated Press isn't naming either girl who is charged because at least one of their attorneys plans to pursue moving her case into juvenile court, where proceedings are closed to the public.

"It's extremely disturbing as a parent and as chief of police," Waukesha Police Chief Russell Jack said at a news conference ahead of the court appearances Monday.

One of the girls' attorneys, Donna Kuchler, asked Pieper to remove reporters from the courtroom Monday because she planned to attempt to get her client waived into juvenile court, but Pieper refused. Kuchler escorted the girl's family out of the courtroom, telling reporters only that the family was horrified at what happened.

The other girl's attorney, Joseph Smith Jr., declined to comment.

Both girls are due back in court on June 11 for a status conference.