'Slender Man' Interrogation Tapes Reveal Shocking New Details About Alleged Stabbing Plot Anissa Weier, Morgan Geyser are heard explaining why they stabbed a friend.

 -- In explosive police interrogation tapes, the two young girls accused of stabbing a classmate in an effort to please the fictional internet character, “Slender Man,” explain in their own words why they believed the character would come after them if they didn't kill their friend.

“I didn’t want to do this,” Morgan Geyser is heard telling a police officer on an interrogation tape. “I was afraid of what would happen if I didn’t... I didn’t want to find out what would happen if we didn’t.”

Morgan Geyser and Anissa Weier, both now 13, were arrested on May, 31, 2014, after allegedly stabbing their then-12-year-old friend Payton Leutner 19 times and leaving her to die in the woods in their hometown of Waukesha, Wisconsin. But after being rushed to the hospital with life threatening injuries, Payton survived.

The police interrogation tapes, which were recorded mere hours after both girls were arrested, were shown at a pre-trial hearing for the girls this week.

“20/20” has been following the case since it began more than eight months ago. This past May, Payton Leutner went to a sleepover with her friend Morgan, and another girl, Anissa, to celebrate Morgan’s birthday.

After her arrest, Morgan told police that Payton was her “only friend for a long time.”

“She was my best friend since fourth grade,” Morgan is heard telling the officer on the interrogation tape.

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But when the officer asked Morgan why she decided to hurt Payton, Morgan replied, “it was necessary” to please “Slender Man.”

Both Morgan and Anissa were obsessed with the fictional character, who is often depicted in fan fiction stories online as a horror figure who stalks children. In court this week, disturbing drawings depicting Slender Man and dismembered Barbie dolls recovered from Morgan’s bedroom were shown.

When asked to describe "Slender Man," Morgan told the detective on the interrogation tape that he was “a tall, faceless man who preys on children.”

“He watches you,” she added. “I’ve never seen him. He’s everywhere.”

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In the interrogation video, the then-12-year-old Anissa said, “He can be anywhere from 6 feet to 14 feet tall... he doesn’t have a face, his skin is white and at his own will he can um like exploit these tendrils from his back and um like strangle his victims.”

Anissa is heard telling police that Morgan suggested they go in search of Slender Man and become his “proxies.”

“Morgan said, ‘Hey Anissa we should be proxies,’ I was like, ‘OK, how would we do that?’” Anissa is heard telling a police officer.

Authorities say Morgan repeatedly told detectives it was “necessary” to kill Payton to become “proxies” of Slender Man and live with him in his mansion in the woods.

They believed his mansion was in the Chequamegon-Nicolet National Forest in northern Wisconsin. Morgan told police their plan to kill their friend began as early as December 2013.

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Anissa told detectives she was excited when Morgan told her of the plan to stab Payton.

“I was excited because I wanted proof that he existed because there were a bunch of skeptics out there saying he didn’t exist,” she said. “Morgan and I were going to be like lionesses chasing down a zebra. I was going to tackle her and then Morgan was going to do the stabbing.”

Anissa also told the detective that it was Morgan who convinced her that she had to kill or else Slender Man would "kill my whole family in three seconds."

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Police said when the girls were caught in 2014, they were carrying clothes, granola bars and water bottles. One of the girls was carrying a picture of her family, telling police she wanted to remember what they looked like after leaving her town for Slender Man’s imaginary mansion in the woods.

The girls told police they left Payton to die in the woods, lying to her and saying that help was on the way. Instead they began their journey to find Slender Man’s mansion.

On the interrogation tape, Anissa described how she felt about Slender Man when they were apprehended, saying, ‘I’m scared. ... I was told if I didn’t do something...my family would be in danger.'”

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Both girls have been charged with one count of first-degree intentional attempted homicide. They have not entered pleas. Anissa and Morgan appeared in court this week before a judge who will decide whether to try the girls as adults or send their cases to a juvenile court. That judge’s decision is expected in March.

“I honestly don’t know why we did this,” Morgan said.