New Details in “Slender Man” Murder Case 20/20 : Season 38 Episode 28

David Muir reports on the trial of two Slender Man-obsessed girls accused of stabbing their 12-year-old best friend and leaving her for dead in the Wisconsin woods. Included: The victim's parents are interviewed, along with first responders and doctors who helped save her life. Also: The bicyclist who found the victim's body takes Muir back to the scene