The trial has begun for a Monmouth County man accused of strangling a former high school classmate during a robbery and throwing her body into the Shark River.

Monmouth County prosecutors said Wednesday that Liam McAtasney thought he was going to get $100,000 from the robbery but only got $8,000. They also say he confessed to the killing of Sarah Stern in a conversation recorded by a friend who was working with investigators.

"Sarah Stern will not be walking through those doors into this courtroom at any point. She will never send her father another text. She will never hug him, or tell him she loves him,” said Assistant Prosecutor Meghan Doyle.

McAtasney’s friend and roommate Preston Taylor has pleaded guilty for his role in the murder. He admitted to helping McAtasney allegedly throw Stern’s body off the Route 35 Bridge into the river. He is considered to be the prosecution’s star witness.

"You don't have to like him to believe him. You don't have to like him to think he's credible," Doyle told the jury.

Taylor described how he and McAtasney plotted the murder. He said that McAtasney said that the money Stern had inherited from her deceased mother was “enough to kill for.”

McAtasney, Taylor and Stern were all former high school classmates and childhood friends. Taylor and Stern were each other’s dates to the junior prom several years earlier.

"This is a girl we talked about robbing and killing and she was in our house, having a conversation. The whole thing just awkward,” Taylor testified.

Taylor also described how McAtasney allegedly killed Stern once he had her alone.

“He went into detail about how he killed her. Said that he strangled her. That it took quite a while for her to actually stop breathing - about a half-hour. And in the process, she peed herself, she vomited. When she started throwing up he stuffed a scarf down her throat. She said his name a couple times,” Taylor said.

Defense attorney Carlos Diaz Cobo says that McAtasney made up the entire story because he wanted to impress a friend who was an experienced horror movie maker.

Cobo is expected to cross-examine Taylor Thursday morning.

McAtasney faces life in prison. Taylor will likely receive a sentence of up to 20 years when he is sentenced after the trial.

Stern went missing in December, 2016. Her body has never been found.

The Associated Press wire services contributed to this report.