N.J. Teen Whose Body Was Dumped off a Bridge Was Allegedly Choked for Half-Hour by Her Friend

"I did something really dumb and planned it out for a half a year," Liam McAtasney appears to tell a friend about the killing of Sarah Stern

In a chilling, secretly videotaped confession played Thursday as part of his ongoing murder trial, a New Jersey man, standing trial for allegedly murdering a childhood friend for the inheritance she’d received following her mother’s death, vividly and calmly recounted strangling her before dumping her body off a bridge — and even complained about the amount of money he walked away with.

The father of murdered art student Sarah Stern sat with relatives, who slowly traced their hands across his back, consoling him as he listened to the accused, Liam McAtasney, 21, detailing his alleged crimes.

At one point in the footage, McAtasney — speaking candidly to a friend who was working with investigators — is heard saying he planned the murder over a six-month period, monitoring Stern’s comings and goings so that he could later imitate those movements for nearby security cameras he’d spotted.

Jurors listened as McAtasney grumbled about only walking away with $10,000, expressing his disappointment as he’d been told by Sarah the amount was closer to $100,000.

“She only had 10Gs, and this money, I don’t know if it’s burnt or something, it’s old money, terrible quality,” he tells his friend, Anthony Curry, who approached police weeks after Stern’s slaying. “I don’t even think I can put it in the bank.”

He continued: “I did something really dumb and planned it out for a half a year.”

The Asbury Park Press recorded the video evidence and posted it to their website.

Sarah Stern/Facebook; Monmouth County Prosecutor's Office/AP

McAtasney continues opening up to his friend Curry. “Her dog laid there and watched while I killed her, and didn’t do anything,” he said. “I choked her out, dragged her to the back, put her in the bathroom, and then I had to go to work.”

In the footage, McAtasney says he strangled Stern and used a stopwatch app on his phone to gauge how long it took for her to die.

“I picked her up and had her just dangling off the ground,” he told Curry. “She pissed herself, said my name. It took me a half-hour to kill her. I choked her out, and she was just laying there, having a seizure.”

He said he stuffed a towel down her throat to prevent her from vomiting, and then pinched her nose for 30 minutes.

In late 2016, McAtasney allegedly killed Stern at her Neptune City, New Jersey, home before driving the body, which he’d placed in the passenger seat of her own car, and drove to a bridge in Belmar.

He told Curry — an amateur filmmaker he had approached a month before the killing for help — he’d parked the car, and started lugging her corpse towards the edge of the bridge when three cars started approaching. He said he tossed her back into the car, and waited for the vehicles to pass.

His roommate, Stern’s former prom date Preston Taylor, was there to drive McAtasney back, and helped him throw Sarah off the bridge. They left her car behind to make it look like a suicide.

Taylor, now 21 but 19 at the time of the killing, has pleaded guilty and had previously testified against McAtasney.

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McAtasney has denied having anything to do with Stern’s presumed murder; her body has never been found.

If convicted, he could be sentenced to life without parole.

McAtasney’s attorney did not immediately return PEOPLE’s request for comment.