Almost immediately after stabbing her classmate in the woods in suburban Milwaukee over the weekend, Anissa Weier, 12, had some regrets.



For months, she and Morgan Geyser, also 12, had been scouring the Internet for stories about a tall, creepy, blank-faced figure called Slender Man, a fictional bogeyman who they insisted was real and lived in a mansion in a nearby forest, according to a criminal complaint charging both girls with attempted murder.



Weier told a detective she thought she would impress Slender Man and be able to go to live with him by killing someone, the complaint said. She and Geyser singled out a classmate in February and began making detailed, ever-shifting plans which they would whisper about on the bus.



On Saturday morning, after having a sleepover with their victim, Weier and Geyser stashed away a kitchen knife and lured her into the woods by telling her they would go birdwatching and play hide and seek.



"People that trust you are very gullible," Geyser told a detective. They passed by a public bathroom and some trees, and then, "Stabby, stab, stab," Geyser said.



But as online fantasy shifted into the real word and Weier heard her victim's screams, she wavered, the complaint said. "I hate you!" the victim screamed. "I trusted you!"



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



Morgan Geyser, the accused accomplice, was not so conflicted: "It was weird that I didn't feel remorse," she told a detective, the complaint said. She later added that it was "probably wrong."



Both girls have been charged as adults in Waukesha County Circuit Court. The victim, whose identity was not released, told the police officer who found her lying on a sidewalk in bloodied clothes she had been attacked by her "best friend." She is now recovering from 19 stab wounds in Waukesha Memorial Hospital.



Doctors treating her said she had wounds to her liver, pancreas and stomach, and that the knife missed a major artery by the heart by only a millimeter, according to the complaint.



Whether the girls truly believe that Slender Man is real is unclear, but both of them described him in vivid detail.



Geyser said Slender Man would watch her and could read her mind. He can teleport, emits radiation that makes you sick and doesn't use computers because they don't work when he's around, she told a detective, according to the complaint.



Anthony Cotton, Geyser's attorney, told an ABC affiliate in Milwaukee his client is mentally ill and should be hospitalized.



"From what I know, we've got a young girl here who has no previous criminal record at all, and if the record is accurate, probably suffers from very serious mental health issues," Cotton said to WISN Television.



Beginning in about 2009, the character Slender Man started to appear in many stories published in online forums, including the Creepypasta.com, a place where amateur writers upload so-called fan fiction, particularly stories about paranormal characters.



On Tuesday, Creepypasta's administrators posted a 3,800 word statement in which they expressed their condolences but said the site is not to blame.



"If we could truly blame any violent crimes solely on one specific form of entertainment as the trigger – well, I suppose it would be a relief," they wrote, "as we'd be able to expunge said cause and clear the world of such awful happenings."



Attorneys for the girls did not respond to a request for comment.