Truly disturbing images have been released including mutilated Barbies and graphic drawings of dead children.
One image read: "I love killing people." There are pages and pages of them, and they're all the more shocking knowing that they came from the diary of a twelve year old girl.
Morgan Geyser and her friend Anissa Weier are accused of stabbing their classmate 19 times leaving her for dead in a park.
The girls claimed a fictional monster known as Slender Man made them do it.
In one just-released interrogation tape, Weier described the stabbing in shocking detail.
She said, "So, I started walking away and then when I was like five feet away, I said, 'Now.' and Morgan said, 'Don't be afraid. I'm only a little kitty cat' and jumped on top of (the victim) and stabbed her repeatedly."
The girls each blamed the other.
One detective asked, "Who stabbed her first?"
Geyser replied, "I think Anissa stabbed her first, and then I continued. And then Anissa said, 'Morgan, make sure she doesn't escape!'"
In their twisted minds, Geyser and Weier told police they believed Slender Man, a faceless long-armed creature popular on the internet, would harm their families if they didn't kill their classmate, Payton Leutner.
Weier told detectives, "She (Morgan) said, 'Oh, and there was one thing I forgot to tell you, I kinda, sorta made a deal with Slender saying that if I didn't, if we didn't kill (the victim) that he would, would either, or could kill our families and everything we love.'"
At one point, Weier lifted her shirt to show blood stains. Left alone in the interrogation room, Geyser passed the time singing.
At a court hearing, Geyser could be seen examining her diary.
We showed the drawings to child psychologist Dr. Jennifer Hartstein. She told INSIDE EDITION, "This was really above and beyond where things looked like they were really crudely severed. Arms, feet, legs - all of these different body parts, and then on top of that cuts and marks on top of the body. It almost looked like the Barbies were being sacrificed before they went after this friend."
Geyser's private diary also included a list of supplies necessary. The list included pepper spray, map of the forest, weapons (kitchen knife), and flashlights.