Filmmaker explains why he helped police record friend confessing to Sarah Stern's murder “[I'll] live with this stuff for the rest of my life," Anthony Curry said.

A New Jersey filmmaker who helped police record his friend’s confession to killing missing teen Sarah Stern said he doesn’t see himself as a hero.

In an exclusive interview with ABC News’ “20/20” anchor Amy Robach on why he worked with police, Anthony Curry, 21, said “I didn't do it for fame and notoriety... I was doing it to bring closure to a family."

Watch the full story on "20/20" TONIGHT at 9 p.m. on ABC.

A Monmouth County jury on Tuesday found Stern’s former classmate and childhood friend, Liam McAtasney, 21, guilty of all seven counts against him, including first-degree murder, robbery, desecrating human remains and other charges. He was accused of strangling Stern, killing her for her money and enlisting Preston Taylor, Stern's junior prom date and McAtasney's former roommate, to help throw her body off a bridge between Neptune and Belmar, New Jersey.

Stern, a promising young artist, was 19 when she went missing in December 2016. Her body was never found, but police discovered her abandoned car on the Route 35 bridge with the keys still in the vehicle.

Authorities say her disappearance started off as a missing persons case and the investigation quickly stalled.

Curry’s willingness to come forward and help police with a sting operation that captured on video McAtasney’s alleged confession to killing Stern is what authorities said led to a big break in their case.

“[Sarah Stern's father] Michael Stern does not get to know what happens to his daughter without Anthony Curry,” Monmouth County assistant prosecutor Meghan Doyle told “20/20.” “I firmly believe that he [Curry] is extremely modest about it and uncomfortable with that role, but to me, he will always be the hero and the reason we were able to bring this case to court.”

“I think we can both agree that Anthony Curry, if he had a choice, would've wanted nothing to do with this situation,” added Monmouth County assistant prosecutor Chris Decker.

Curry first met McAtasney in high school and said the two became close friends, bonding over music, movies and the TV show, "The Sopranos." Curry said he “practically lived” at McAtasney’s house and that they hung out together often.

On Thanksgiving 2016, a week before Stern’s disappearance, Curry, a film director, said McAtasney told him an idea for a movie while they were hanging out at McAtasney’s home.

“I'm a filmmaker. He used to tell me ideas all the time about films I should make and all that stuff. And he told me about this idea he had to kill this girl ... that he was going to strangle her and throw her over the bridge with his friend,” Curry recalled.

Curry said he never believed his friend was discussing a real murder plot.

“I was like, ‘Yeah, he's a little nuts.’ But I don't know, I just thought it was a movie. He would tell me ideas all the time and that stuff,” he said.

Curry said he later had learned of Stern’s disappearance on social media. But didn’t think anything of it until he said McAtasney began contacting him almost daily, saying he wanted to meet with him.

“[He said] that it was urgent ... ‘I got to tell you something,’” Curry recalled.

Curry said McAtasney began to communicate primarily through Snapchat, a social media app where messages disappear.

He began to think McAtasney’s idea wasn’t just a movie plot, Curry said, "when he asked me if the cops questioned me about him" regarding Stern's disappearance.

Curry testified he took a picture of that Snapchat message.

While he said he didn’t feel like his life was in danger, Curry said he thought his family's safety could be.

“If somebody is capable of doing that, he could try to hurt my family or somebody I knew ... kid’s wacko,” said Curry. “You don't believe somebody would do something like that. So, it's heartbreaking in a sense. Somebody who's your good friend, you don't think they would do something like that. It was an innocent person.”

In January 2017, Curry went to police with details of his Thanksgiving conversation with McAtasney. Police asked Curry to participate in a sting operation involving taping conversations with McAtasney to see if he would confess to killing Stern. Curry agreed.

Police set up audio and video recording devices in Curry’s car and the pair met at a favorite hangout spot in Bradley Beach, New Jersey.

“They told me, 'you gotta act sort of like [the movie character] Donnie Brasco.' You gotta ask him questions,” Curry said.

McAtasney is seen in the video giving Curry a pat down to see if he is wearing a wire. Curry said McAtasney began to tell him what happened almost immediately.

“He wanted to tell me. I think he wanted to get it off his chest. For some reason he trusted me,” said Curry. “He was happy to see me. It's like seeing an old friend, but he was different, I don't know. It was like somebody I never met before. It was almost like meeting a brand-new person. It was a weird, strange. He told me I was the only person in this world that knew besides Preston [Taylor].”

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At McAtasney's murder trial, the video was played for jurors and served as a key piece of evidence for the prosecution.

“It took me half an hour to kill her,” McAtasney can be heard saying in the tape.

“The worst part of it is I thought I was walking out [with] $50,000 to $100,000 in my pocket,” McAtasney continues in the tape. “She had one safe that she took money out [of], and she only had $10,000.”

McAtasney’s defense attorney, Carlos Diaz-Cobo, argued that his client believed what he said on that the recorded conversation with Curry was for a movie audition, which Curry denies.

“That wasn't no movie audition. That's real life. Trust me, I worked in film for years. I know the difference between reality and fiction, and that's reality. That's real life. No matter how sick you think it is or whatever, that's real life,” he said.

Prosecutors said McAtasney, who did not testify at his trial, planned Stern’s murder for six months. McAtasney believed Stern had found more than $50,000 in cash hidden in a box in her family’s second home, authorities said.

Prosecutors argued that McAtasney killed Stern in order to steal that money which she had discovered after her mother died from cancer in 2013 and then later enlisted Preston Taylor to help him remove her body from her home and throw her into the Shark River in New Jersey.

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Stern's father, Michael Stern, also told "20/20" that if Curry had never come forward, "we probably never would have got an answer" as to what happened to his daughter.

"It was a tough decision for him. He didn't have to come forward," Stern said.

Taylor, who testified against McAtasney at trial, pleaded guilty to first-degree robbery, second-degree conspiracy to commit robbery and second-degree disturbing or desecrating human remains. Taylor admitted to his role in the robbery.

Both he and McAtasney are expected to be sentenced in May.

Curry said he came forward because he felt that it was the right thing to do.

“[I’ll] live with this stuff for the rest of my life,” said Curry. “Back then he was a great friend, one of my best friends. He'd give you the shirt off his back. Now, [he’s] dead, a killer."