Transcript for New Jersey man shows police how he disposed of his friend Sarah Stern's body
Reporter: This week, justice in a New Jersey courtroom. Guilty. Guilty. Guilty. Reporter: Leah, a former friend of Sarah stern, found guilty on all counts of murdering the 19-year-old who went missing from her home in December 2016. A jury determining that he strangled her and enlisted her junior prom date, Preston, to help throw her body off a nearby bridge. To think that somebody who pretended to be her friend actually did that to her and without any remorse. It's just, it's painful, it's sad, and it's just, it's beyond anything that I've ever experienced before in my life. Reporter: Prosecutors say the motive, getting their hands on Sarah's lock box, which he believed was stuffed with up to $100,000 in cash. I picked her up under the shoulders and hoisted her up. Reporter: And now newly-released video shows that accomplice, Preston Taylor, walking investigators through exactly what happened after the murder. I carried her over here. Dragged her over here and kind of sat her under the bushes right here. 911, where's the emergency? Reporter: It was a 911 call on a December night that first indicated something had gone terribly wrong. I'm actually on the belmar bridge, there's a car abandoned. Is there anyone in the No. The phone rang in early in the morning, do you know anything about a car, a gray oldsmobile? Yeah, my daughter drives that car. A million things go through your mind. Reporter: You were in Florida. Yeah. Reporter: You drove from Florida back to New Jersey. At 3:30, 4:00 in the morning, there's no traffic. You can drive pretty quick. Reporter: Less than two hours after that 911 call, police bang on the door of his home. There's a unique reality and a great one, where the police when they go and interview people they have body cameras on. Liam, do you have a second? Can I come in and talk to you real quick? No problem, officer. Is Sarah here by chance? No. When's the last time you talked to her? It was earlier today. What was her mind-set when you were talking to her? I just know she was trying to get away. Reporter: Early in the investigation, they both suggested that Sarah may have left town or taken her own life. Had she been different than normal lately? And for how long? In the past, she has had a tendency to have self-destructive, suicidal What do you think happened? I think she jumped. Reporter: The investigation stalls. It's horrible. It's a sense of hopelessness. You don't, you have no idea. Sarah's my only child. And it's a hard feeling that we couldn't find her. Reporter: She had just disappeared. Just vanished. Reporter: But then the police receive a tip that leads them to a sting operation, using another friend. This video secretly recorded by She goes to walk out the front door. I choke her out. Drag her. My biggest problem was the dog. And her dog laid there and watched as I killed her. Didn't do anything. Her Dog. And it took me a half hour to kill her. I thought I was going to be able to choke her out and have her out in like couple minutes. 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. Reporter: Prosecutors playing that video during the murder trial, arguing money was the motivation, intent on getting a safe inside Sarah's home. The worse part of it is, I thought I was walking out, $50,000, $100,000 in my pocket. She had one safe, and she took money out, and she only had $10,000. He literally gives a blow-by-blow of how he killed her, where he killed her, how long it took him to kill her, how they moved the body, where they hid the money. I mean he really just does a who's who of this crime on camera, which I will tell you, is the perfect way to capture it, because you're not in an interrogation. He thinks he's talking private privately to one guy. Reporter: His accomplice Taylor later walked investigators through the crime scene. The kitchen and living room lights were on. Okay. And this door was closed. This one I couldn't get open, but I was able to push this one open. Enter, and Sarah was slumped in this corner right here. Reporter: Explaining how the two disposed of her body. These are the bushes that you placed Sarah in? Mm-hm. Right under these bushes here. We pulled her out. And he picked her up to start dragging her. I grabbed her legs and got her over to the fence. Liam dragged her over to the car and sat her in the passenger seat while I was putting the safe in my car. Did you see him dragging her? Yeah. If somebody were driving down the road and looking into that car, what would they see? They would have seen Liam driving the car and Sarah, assuming she was asleep asleep in the passenger seat. Reporter: Taylor said he was driving his own vehicle. Which bridge? The 35 bridge. Reporter: The bridge is where Taylor told authorities they threw stern's body into the water below. Her body was never found. Sentencing for both men is set for may. For Sarah's family, more than two years after her murder, finally, a sense of justice. How do you want the world to remember Sarah stern? Well, I'd like to have her be remembered as an artist. A friend. That was just, you know, a good person. And that's, that's all that was really about. Reporter: For "Nightline," I'm Amy robach in Neptune city, New Jersey. Our thanks to Amy. The 2020 special with friends like these areas tomorrow night at 9:00, 8:00 central here on ABC.
This transcript has been automatically generated and may not be 100% accurate.