Transcript for Coach allegedly threatens student in hostile emails, phone calls and outside her class: Part 4
Reporter: It's an April morning in 2015 baillie Gibson and her fellow shot put thrower Julie Labonte are roommates living alone in this off campus house. But they're about to get company. He came to the house and he was knocking on our door. Reporter: It's their volatile track coach Craig Carter. Remember the evening before he allegedly threatened baillie with a box cutter. What was he saying? We acted like we weren't there. But he knew we were, 'cause he was sending me texts like I'm outside, you haven't left your house since 6am, I know you're inside. You better answer. You better come answer. And he was walking around our house. Every single window he tried, every single door. What was he saying when he's out there? "I'm in front of your home. You better have your gun because I brought mine." And then we're very, very scared so we're actually going around the house just to make sure everything is locked. We're like, "Is he going to bust out the door and come in and then shoot us?" Reporter: The two terrified young women barricade themselves in the bathroom. While baillie gets text messages like this, "You tell the cops and it won't end well for you." How scared were you? Scared. We sat in the bathroom and we were both crying and we didn't have anything to protect ourselves. Were you afraid you were going to die? Yes. Did you think of calling the police at that moment? You're in the house, he's outside circling the house. Why didn't you just call the police? Could they really protect me? In an e-mail he says, you think the cops can get to you faster than I can? If I'm breaking through your house and I have a gun loaded coming at you, you think they're gonna save you? Reporter: She says after about an hour of prowling around outside the house, Carter finally leaves. And soon issues a warning shot of sorts. Later that same day, Craig Carter sent a text to Bailey Gibson, with what appeared to be a gun barrel in his mouth and the message, "Bye, I love you." Now he later said that it wasn't a gun barrel, it was just a pipe. But if you're baillie Gibson in that moment I'm sure it was unnerving, to say the least. Reporter: Then about 30 minutes later another text. "I didn't have the balls to pull the trigger. You win." For baillie's best friend Julie it is the breaking point. She's had enough. And decides it's time, time she says they turn the tables on their tormentor of a track coach. She helps baillie hatch a plan to secretly record him. I told baillie, I'm like, this is not right what he's saying. You should take your phone honestly and record this and send that to the authorities. You want her to have evidence? Yes. Reporter: So when Carter angrily calls Julie's phone looking for baillie they secretly hit the record button. Thenly way I could get your attention is if I -- threatened. Here I'm the bad guy, because I threatened. You should have never put your hands on me. Well, actually I probably should have killed you. Reporter: For more than an hour Carter threatening and desperate. I wanted you to love me. You were in a Game with me the whole time. That is wrong man. I'm going to make you pay. I know exactly where you're going to be. Every day. So don't tell me that you're going to call the cops. Because I'm going to bust through your window, with a shotgun loaded coming right at you? You gonna call 'em real fast? Think they'll get there in time?" I just want to hold the pistol to your head and then what? I guess you would have to blow me away, right? Should we try that? It was an incredible phone call in that he made several damning threats. Trying to get baillie Gibson to meet him one last time for a sexual encounter. I make sure I You one more time. Reporter: Baillie agrees to meet her coach later that week but Carter doesn't leave her alone instead sending her a series of hostile e-mails. I'm like a mountain lion who stalks his prey before he kills. We will see if you're smart enough to do what's wrong or what will cost you your life. Craig Carter's action were not rational by any measure. This is a guy who was coming unhinged and the e-mails he sent to baillie were so graphic and so disturbing unlike anything I've ever seen a coach send an athlete. Reporter: Two days later coach Carter ambushes her outside one of her classes. I turn around and he's right behind me and had this smirk on his face like I caught you. I said I don't want to talk to you and he said you can either do this the easy or the hard way. Reporter: There are plenty of witnesses. One student even calling 911. University police this is Claudia. Harassed by a male? Yes. He was saying things like you need to leave here with me and like trying to pull her away. Reporter: Thanks to that 911 call campus police are now actively investigating. At that point the university of Arizona was coming to grips with the fact that one of its coaches had issued some serious, serious threats to a student athlete. Reporter: It doesn't prevent Carter from sending baillie this e-mail. You just dug your grave. Baillie says she had become numb to his threats but this one is unlike any other. That's what I should take away, something that matters to you like your mom. I don't have to hurt you, I can hurt somebody else that means a lot to you. I could have cared less if he killed me but when he brought in my family and friends that was the main part that was like that could happen. Reporter: Finally baillie calls her mother and reveals her deep secret. I was crying. I would tell her everything at that point. I'm so distraught. I was like I just want you to love me. I don't want you to think bad of me. She arranges to meet up with her parents in Las Vegas. I just held her and she cried. That night we went to bed and she woke up I don't know how many times screaming in the night. It was don't kill my mom, don't kill my mom. She said I didn't tell you because I didn't want you to quit loving me. That's hard. Reporter: Next, coach Carter is in the interrogation room. Turning the tables. She was the one that was, you know, kind of coming on to me. Reporter: And surprising texts from baillie that appear to bolster his claim. Reporter: To some people that sounds like a girl who maybe has a crush on her coach.
This transcript has been automatically generated and may not be 100% accurate.