WATCH: Filmmaker who knew Sarah Stern's childhood friend breaks case wide open: Part 6

WATCH: Filmmaker who knew Sarah Stern's childhood friend breaks case wide open: Part 6

Transcript for Filmmaker who knew Sarah Stern’s childhood friend breaks case wide open: Part 6

To help protect yourself from another dvt or pe. Talk to your doctor about Xarelto??. This is a girl who has gone off the grid and no one knows why. She either committed suicide or staged a suicide. Dude, if you know where this girl is, you have to let us know. I’m one of her closest friends and I have no idea. She discovered a shoe box full of cash. She sealed her fate with that money. I thought I was walking out 50 grand, 100 grand in my pocket. He was doing an audition. What are going to live some boring ass life? ?????? It’s almost two months since Sarah’s gone missing. Her car has been found but no other real sign of her and no concrete leads. Can you describe for me as a father what it was like during those two months, the not knowing? It’s horrible. It’s a sense of hopelessness when you don’t — you have no idea. Sarah’s my only child and it’s a hard feeling that we couldn’t find her. Michael stern was trying to find his daughter. Michael stern was very persistent. Michael stern was not sitting by without checking in with law enforcement and demanding to know what we were doing. It’s breaking my heart to not know where she’s at. Police have hit a wall until they get a phone call from a former classmate. Someone who went to high school with Sarah stern and he has quite the information to share. Anthony curry is an aspiring film director, and he went to high school with Liam and Sarah. Tell me when you first became friends with Liam. We didn’t get real close until like junior year of high school. He liked “The sopranos.” We played music together. Why did you go to police? Just doing the right thing. Anthony told us that he had wanted to talk to us about the information that he had. Anthony had told us that on thaens Thanksgiving evening, which was November 24th, that he had went to Liam’s house in Neptune city and that while there Liam had informed him what he planned to do to Sarah stern. He tells you it’s an idea for a movie. A plot for a movie, yeah. I make movies. I’m a filmmaker. He used to tell me ideas all the time about films I should make and all that stuff. He like told me about this idea he had to kill this girl. He was going to like strangle her and throw her over the bridge with his friend. Did he seem excited about this idea? Yeah, he was like hyped. He was an energetic kid. I was, like, he’s a little I don’t know I just thought it was like a movie. What are the chances that mcatasney would float this earlier, and then Sarah stern would end up being murdered in prisely the same terms? So, Anthony doesn’t really give it another thought until it comes up on social media or the news that she’s missing. If anyone has any information on the where abouts of Sarah stern, please give please a call. In January 2017 he had started receiving Snapchat messages from Liam mcatasney. How often was he trying to contact you during that time when Sarah went missing? Almost every day. What was he texting you, what was he saying to you? That he wanted to see me. That it was like, urgent. We saw Anthony curry’s demeanor with the way he was providing us the information. We saw the concern that he had. He was scared. Did you feel like your life was in danger at all? If somebody is capable of doing that, he could like try to hurt my family or somebody I knew. So police hatch a plan to catch Liam mcatasney and they cast Anthony curry in the starring role. Detectives equip his car with a video recording device, and this is going to be their sting operation. For Anthony curry this is a risky move. He is making up a story about why he needs to meet with Liam. Everyone’s got to be nervous about this meeting. The person’s car you wired usually has to drive a distance. They’ll sing. They’ll hum. They’ll turn on the radio. They’re nervous. I mean this is a big deal. They’re actually going to try to get a person to talk about a murder they committed. Liam had traveled in his own car. Parked his vehicle in a parking ace several down from Anthony and had gotten into Anthony’s car. What’s up, man? How you doing? We were listening live through electronic equipment. You want a cigarette? No I quit that . Were they telling you what to say? They did say you know you gotta act sort of like Donnie brasco. You gotta ask him questions. As soon as he got there. He felt me down for a wire. Liam, dude, you can’t blame me for doing this right? I gotta feel you up bro real quick, right? No disrespect. What were you thinking then when he did that? Real. And he just spills his guts. I didn’t really have to do much work, like he wanted to tell me, you know. I think he wanted to get it off his chest. Yeah, I got the FBI on my Dude. About what? About killing Sarah. They’ve been — they were up my ass. First it was just normal police, they were on my ass. And I, I had to go in and get interrogated by them multiple times. But then it kept moving up levels. And now it’s a federal case. That’s not even the worst part. The worst part of it is, I thought I was walking out fifty grand, a hundred grand in my pocket. She had one safe and she took money out. She only had ten grand and this money — I don’t know if it was burnt or something. It’s Old money. Terrible quality. I don’t even know if I can put any of it in the Bank. So where do you have it? Hidden or something? Yeah. Where did you hide it? Sandy hook. First it was in my house for a long time, but then I stopped trusting Preston. We threw her out the bridge. Not only does he implicate himself in this, but he mentions somebody else who helps him dispose of the body. Police didn’t know about that. They didn’t even suspect that. She goes to walk out the front door. I choke her out. Dragged her. My biggest problem was her dog. And her dog laid there and watched as I killed her. Didn’t do anything. Her Dog. I’ll never forget the way that he talks about how her dog just laid there as I killed her. That was, to me, the most disturbing thing I’d ever heard in my life. I picked her up and had her just like dangling off the ground and she just Herself and — Cause you lose control of your bowels. Said my name and then that was it. And it took me a half an hour to kill her. I thought I was gonna be able to choke her out and have her out in like a couple minutes. It’s heartbreaking in a sense you know, somebody who’s your good friend, you don’t think they would do something like that to an innocent person. It’s disappointing. I got a shirt and I just shoved it down her throat so she wouldn’t throw up or anything and held my finger over her nose and set a timer. It was nauseating. How anyone could talk the way Liam spoke about Sarah and Sarah’s death was very disturbing. You are the only person on this planet that knows, besides Preston. And Preston doesn’t know that you know. I’m not no Rat, bro. It could be anyone. And I don’ T want Preston to, to think that he has to kill you and take you out because you are the only person that knows. Movie, man. Yeah and I didn’t get a lot of money, but I had enough money to just be like living comfortably in my house. Throwing parties all the time. The most egregious thing that I heard was how Liam didn’t feel any different after doing this. What, you’re gonna live some boring Life? What were you thinking? He did a terrible thing. That’s really all there is to it. He did a terrible thing. When you saw the video, what was your reaction? My head hung. I have children. First thing I thought was how Michael stern is going to feel about this when he finds out exactly how his daughter died. The second thing I thought, being a career prosecutor is this is great evidence. It was good talking to you, bro. Good talking to you. Take it easy, bro.

This transcript has been automatically generated and may not be 100% accurate.

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