WATCH: Liam McAtasney's roommate admits to helping dump Sarah Stern's body: Part 7

WATCH: Liam McAtasney's roommate admits to helping dump Sarah Stern's body: Part 7

Transcript for Liam McAtasney’s roommate admits to helping dump Sarah Stern’s body: Part 7

Detectives in monmouth county, New Jersey, have just recorded what they say is an undeniable confession to murder. How you doing? You want a cigarette? After the consensual recording concluded, we had regrouped and had a briefing and we had listened to the recording that night. I choked her out. She was having a seizure or something. He literally gives a blow by blow of how he killed her, where he killed her, how long it took him to kill her. It took me a half hour to kill her. How they moved the body, where they hid the money. He also mentions his roommate and his partner in crime, Preston Taylor. We had made a decision to locate Preston first. We had learned that Preston would be traveling to brookdale community college in linkroft. We had conducted a motor vehicle stop of his vehicle. Once we stopped his car we had detained Preston and transported him to the mammoth county prosecutor’s office. We know what happened to Sarah. We know what your involvement in it was. We want to know why Liam did what he did. What did he do? He killed Sarah. You know that correct? Yes. I don’t know if I’ve ever seen anyone confess that quickly. I mean that — that’s really the reality of what happened with Preston Taylor. And then he just goes on for, you know, 52 pages or something in a transcript of describing everything that they did. I got home just as he was getting ready to run out the door for work and he was like, “Dude, I did it.” What did you take that to me? I take it as he killed Sarah. He said that her body was still at the house and we had to get rid of it tonight. Preston takes police back to what he says is the scene of the crime, Sarah stern’s house, and he reenacts what he says he and Liam did that night. We’re here for the purpose of doing a walk through of Sarah stern’s residence, is that correct? Correct. It’s powerful. He was willing to go back there, to this place where he had done some pretty awful things, and show the detectives how they did this, and how they did that. 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. She was sitting like this, tucked into the corner, and leaning over the toilet. So Liam has Preston go back to Sarah’s house and move Sarah basically out of the house to the bushes. Will you just show us how you were positioned when you were taking her out? She would have been facing away and I had my arms under her shoulders. Were her feet dragging on the ground? Yeah. Then I carried her over here. And, kind of sat her under the bushes right here. It’s interesting because he’s basically like a flat line. It comes across as very matter of fact and cold, as to exactly what they’re doing which is a very, very gruesome crime. Now why did Liam come back here with you? What was your purpose in being here? To move Sarah’s body too. Liam went inside the house to get the safe. And he gave me the safe. And I put the safe back over by where we jumped the fence. They drag Sarah’s body out from under the bushes, drag her to a fence. It almost brings you back to that point, where you can see him dragging her, and they just toss her over like nothing. Hoisted her up and over, threw the safe over, the two of us jumped over, and I got in my vehicle and Liam got in Sarah’s vehicle. He only took responsibility for assisting with disposing of Sarah’s body over the bridge, but he was very cooperative in the fact that he had taken us to multiple locations where the safes were buried. Where is that safe now? Buried in the shark river park. Did you bury it or did Liam? Liam did. Liam did. With the money? No. Where’s the money? Money’s in another safe. Preston had viewed some maps and was able to identify general areas where these safes were buried. Detective weisbrot called me, “Hey, you wouldn’t believe this, we got some new information on the Sarah stern case.” This is what’s going on. This is where you need to go. We ended up caravanning to sandy hook. Once we had traveled to sandy hook he had directed us to the lighthouse and the location where the safe was buried was just east of the lighthouse. The area that that safe was buried, it was pretty nondescript. It was all overgrown. So as we were going down we’d stop, photographed some more Preston was handcuffed and shackled. He was directing the forensic detectives who were down in the pit as to where the safe was buried. Just a little bit to the left of where we were digging, and there’s the corner of the safes just sticking out of the ground. So detectives find buried in the dirt a small gray century safe with the number 002 stamped on it, and just a short time later, another set of police officers make the arrest of Liam mcatasney and they search his car. On his key chain he had a century safe key and on the back side of it it had 002. The fact that Liam had the safe key, for the safe that was buried with Sarah’s money at sandy hook is an amazing piece of evidence. And low and behold, he used one of them to open the safe. What did you find inside that safe? $9,350.00. In cash, 100s, 50s and 20s. Police now have enough evidence to charge Liam with murder. Liam is arrested while we are in the shark river park with Preston. We had went in and made an effort to speak to him we had asked him if was retained by an attorney and he had indicated that he was as a result of that we did not interview Liam at that point. I think I’d rather not speak to anyone until I talk to him. Okay. Perfect. Thank you very much. Walked in and the detectives, they were there. They said just sit down we want to tell you something. This was someone who said he loved Sarah, who was in your home. That was not Liam, to me, describing an actual murder. I had planned Sarah’s situation for me to be interrogated by cops. That was an act. What are they watching if not a confession? He was making things up. Trying to impress the horror film director. This is like a

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

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