Tonight on '20/20': Mothers of Slender Man attackers open up - WKOW 27: Madison, WI Breaking News, Weather and Sports

Tonight on '20/20': Mothers of Slender Man attackers open up

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Abe Van Dyke via ABC 20/20 Abe Van Dyke via ABC 20/20

WAUKESHA (WKOW) -- Standing in a Wisconsin police station lobby, Angie Geyser said she was in disbelief when detectives, who had just interrogated her daughter, told her that her 12-year-old had admitted to a stabbing a classmate and leaving her for dead as part of a plot she and her friend had planned for months.

“I couldn't believe what I was hearing,” Angie Geyser told ABC News’ “20/20.” “I never would have imagined that my daughter was capable of hurting another person.”

(Watch the full story on ABC News "20/20" FRIDAY, FEB. 2 at 9 p.m. on WKOW 27 or later on the 20/20 website

It was the case that rocked the town of Waukesha, Wisconsin, and stunned the nation: Two then 12-year-old girls, Anissa Weier and Morgan Geyser, arrested on May 31, 2014, for stabbing then 12-year-old Payton Leutner, with the intent to kill her to appease the online fictional character, "Slender Man." Prosecutors have said that both Weier and Geyser were obsessed with the character, who is often depicted in fan fiction stories online as a horror figure who stalks children.

Payton, now 15, crawled to a nearby road and was helped by a passing bicyclist before she was hospitalized with life-threatening injuries. She survived the attack.

Both girls' mothers told "20/20" that they never saw any warning signs from their daughters that they would harm someone else.

“They [Morgan and Payton] would sit up in Morgan's room and they would do each other's nails, and they would laugh, and make a mess," Angie Geyser said. "They were just typical girls.”

Morgan’s mother said she knew about her daughter’s fascination with Slender Man and talked about it with her.

“She would show us some of the pictures, and she would read us some of the stories, and while some of the subject matter was a little dark, I wasn’t concerned,” Angie Geyser said. “When I was Morgan's age, I was reading Stephen King novels. I remember being 11 years old and riding home from the library with [the book] 'IT' under my arm. And that's a very scary and dark story, so I just thought it was normal for a child of middle school age to be interested in scary stories.”

But Anissa's mother, Kristi Weier, said her daughter “never mentioned anything to me about her belief in Slender Man.”

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