Morgan E. Geyser was allowed to have two friends over every year for her birthday. This year, she'd celebrate on May 30. That is the day she and Anissa E. Weier, both 12 years old, would try to kill their friend during a sleepover.
On Monday, the two Waukesha, Wisconsin, girls were charged as adults with attempted first-degree intentional homicide.
Their victim, another 12-year-old from Waukesha, was stabbed 19 times by either Geyser or Weier or both, according to a criminal complaint. All three attended the same school.
Geyser and Weier were held on $US500,000 ($A540,979) bail each. The girls attempted murder, they told police, to pay homage to a fictional character who they believed was real after reading about him on a web site devoted to horror stories.
On Saturday, a bicyclist found the victim on the footpath, covered with blood, with injuries to her arms, legs and torso. She had managed to crawl out of the woods, where the suspects allegedly had left her to die. She was rushed to a hospital where she was reported to be stable on Monday evening, but fighting for her life.
A Waukesha County Sheriff's deputy found Geyser and Weier hours later. A knife with a five-inch blade was in Weier's backpack, police said.
Police said suspects explained the stabbing referencing their dedication to “Slender Man”, a character they discovered on a web site called “Creepypasta Wiki”, which is devoted to horror stories.
According to police, Weier said Slender Man is the “leader” of Creepypasta, and in the hierarchy of that world, one must kill in order to show dedication to Slender Man.
Weier said that Geyser told her they should become “proxies” of Slender Man and kill their friend to prove themselves worthy of him.
The suspects believed that “Slender”, as Weier called him, lived in a mansion in the Nicolet National Forest in Wisconsin.
The plan was to kill the victim and walk to Slender's mansion to become a proxy.
After school on Friday, police said, Weier said she and Geyser went to Weier's house, where she packed a backpack before they went to Geyser's house.
With Geyser's father, they picked up the victim and all went to a skating rink in Waukesha.
They came home around 9.30pm, and went to sleep in Geyser's room. Geyser and Weier originally had planned to commit the murder at 2am early on Saturday, according to the criminal complaint.
They'd duct tape their victim's mouth, stab her in the neck and pull the covers over her to make it look like she was sleeping.
Then, they'd run. But the plans changed after they'd been out roller skating Friday night. Instead, they'd try to kill her in a bathroom at a nearby park the next morning. Weier knew there was a drain in the floor for the blood to go down, she told police.