Transcript for Slender Man: Police Hunt for Young Girls Accused of Stabbing Their Friend
Wisconsin. Just outside Milwaukee. Tonight, in the depths of a brutal winter blast -- but they're also dealing with something else. The gruesome new details emerging just this week about a horrific tale that began to play out on a Saturday morning this past may. A birthday sleepover with three 12-year-olds the night before -- and now two girls are missing. The other, Payton leutner, has somehow crawled out of the woods, covered in stab wounds. 19 of them. She is wheeled into the operating room -- and just this week, more than eight months after that moment, the pretrial hearing. And we're now hearing from detectives who tried to talk to her the moment she was brought in. It seemed that it hurt too much for her to talk. She had a hard time breathing. Reporter: Outside that hospital, in that town -- A major search by ground and air. These are the woods where the stabbing actually happened. Police are still on the scene. Reporter: A frantic search for the two missing, Morgan geyser and Anissa Weier. Two 12-year-old girls stabbing their friend nearly to death is unimaginable anytime, but especially for a safe community like the city of waukesha. Reporter: So unimaginable that even the brother of one of those missing girls, at first, confused, fearing for her safety too. Showing reporters photos of his sister. Asking, have you seen her? That's her, that's Anissa, she's been missing for I don't know how long now. Reporter: While back at the hospital, where they ask us to put on scrubs to enter the O.R., surgeon John Keleman is about to discover how much damage has been done. He tells me about one of the stab wounds to the heart. The knife came directly down at this point where this large branch was coming off this major artery. And cut through the tissue overlying it, so that the vessels were totally exposed by this injury. Reporter: The knife cut through the tissue but not the artery itself. Exactly. The knife stopped at the wall of the artery. Reporter: And had it not? Had it not, she would have had a major heart attack from the amount of bleeding and probably died within a minute or two. Reporter: That close to death. But they were now saving her life. While the hunt for the other two girls is in high gear. Every agency in the area searching. We had the waukesha county sheriff's department, the city of waukesha police department, new Berlin police department, city of waukesha fire department and flight for life all scouring that area. Reporter: Then, nearly five hours after Payton crawled out of those woods, the two other girls are found. They were right here, along interstate 94 heading out of waukesha. A knife with a five-inch blade found in one of the girls' bags. And just this week in court, we heard from the officer describing Anissa Weier as she is taken into custody. I asked her to show me her hands and she complied. And then I asked her to walk towards my voice. I noticed there was some staining on her sweatshirt, or on the abdomen area. Reporter: And Anissa in her own words describing the moment she was found. I said, I'm scared I was told, I was told if I didn't do something my family would be in danger. Reporter: Neither girl puts up a fight. They would soon be questioned. And we now hear Morgan describe the victim, Payton, as one of her closest friends. She's was my best friend since fourth grade. Who was? Payton. So why did you pick Payton? I didn't pick her. Reporter: And as Morgan is being questioned, that friend Payton was coming out of surgery. And when that surgeon comes out what did he reveal? He said, "So we had to crack her chest." It was awful to hear that she had to go through that. Reporter: How close do you think she was to losing her? If the knife had gone the width of a human hair further, she wouldn't have lived. Reporter: Human hair. What is that, a millimeter? Less than a millimeter. Reporter: Between living and dying. Yes. Reporter: Where on Earth do you think she got the strength to crawl out of those woods? Well, we asked her and she said, "I wanted to live." Reporter: At first, Payton couldn't talk. Writing to communicate. Do you remember the first message she wrote? "I want to go home." Reporter: "I want to go home." "When can I go home?" Reporter: And has Payton talked at all about the horror of that moment? She told me she was scared, but the first time I asked her what she remembered about what happened, she said, "All I remember is the pain." Reporter: The pain. And they would reveal to me there was something else she asked. "Did they get them?" We told her they were -- they were found and the police have them. Reporter: And as a dad, in that moment, how hard was that? Harder than I would have ever been able to imagine. This is my little girl who's laying there, and the only thing that I could tell her, at the time, to make her feel better was that the police have them. And she was safe with us. Reporter: His daughter terrified of the two girls who were her friends. How well did you know these -- these two other girls? Oh, they were best friends. They were best friends since about fourth grade. Fourth grade is when we met Morgan for the first time. Reporter: They say Payton would talk to Morgan every night on the phone. Were there ever any red flags? They would have little arguments. But every 12-year-old girl has little arguments. Reporter: The other 12-year-old, Anissa Weier, they had not met, but they say Payton knew her from school. And as Joe and Stacie reassure their daughter the girls have been found, police were questioning them. What did they do to their friend? And even more disturbing, why did they do it? Tonight, Morgan, for the first time in those interrogation tapes, seeming to waver. I didn't want to do this. Why did you do it then? Because I was afraid of what would happen if I didn't. Reporter: And Anissa also fearing what would happen if they didn't do it. I was really scared knowing that slender can easily kill my whole family in three seconds. Reporter: And just lien to the detective who was questioning her. When Morgan said to you that if we don't do this for slender, our families or loved ones are going to be killed. Do you honestly believe that? Well, yeah. Reporter: When we come back -- the bone-chilling plan emerges. The plan was to murder her. She wasn't suppose to make it out alive. They told police they wanted to kill the victim so people would know that slender man was real. Reporter: Who is this mysterious, fictional character born on the internet? As we hear from those girls -- now in their own words -- about what it was that drove them to do this. And we see the alarming images found from inside one of the girl's bedrooms. Right near the dolls, the bed, the clothes -- there was something else.
This transcript has been automatically generated and may not be 100% accurate.