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DAVID MUIR REPORTS NEW DETAILS IN "SLENDER MAN" MURDER CASE

"20/20" Airs Friday, February 20, on ABC

What started out as a normal middle school sleepover took a horrifying turn when one 12 year-old girl was stabbed 19 times by her two best friends and left for dead in the Wisconsin woods. The girls' motive and the miraculous recovery of the survivor made headlines around the world since the May attack. Just this week, new details have emerged in the trial. "20/20" goes inside the interrogation room to hear Morgan Geyser and Anissa Weier in their own words describe what they did and why they did it. Plus, twisted drawings depicting death and dismembered Barbie dolls recovered from Geyser's bedroom give a peek into her mind. Also, investigators recount what they found when they looked at the girls' cellphones and computers - including the internet search "how to get away with murdering someone." David Muir's report airs on "20/20," FRIDAY, FEBRUARY 20 (10:01-11:00 p.m., ET) on the ABC Television Network.

The victim's parents revealed for the first time to David Muir the chilling details of the incredible sequence of events that, against all odds, led to their daughter's survival. Where and how did she get the strength to fight off death? Muir's report also includes interviews with the first responders and doctors who helped save her life, as well as the bicyclist who found her - and who takes "20/20" back to the scene.

The two other girls, who are both charged with attempted first-degree intentional homicide, say they attacked their friend because they wanted to prove themselves to the mysterious, fictional internet character called "Slender Man," who they believe to be real. Who is "Slender Man" and why should parents be aware of him?

"20/20" is anchored by Elizabeth Vargas and David Muir. David Sloan is senior executive producer.