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Four Las Vegas teenagers who beat their high school classmate to death have escaped a lengthy sentence for murder after striking a plea deal.

Jonathan Lewis Jr, 17, died in hospital days after he was stomped, kicked and punched unconscious in an alleyway last November.

His killers, aged 16 and 17 at the time of the attack, were to be tried for second-degree murder in adult court, but admitted manslaughter in a plea deal that will see them spend an unspecified period in juvenile detention.

The victim's mother, Melissa Ready, told local media: "There's literally no one being held accountable with true punishment for my son's murder. It's disgusting."

She told the Las Vegas Review-Journal she opposed the deal and was not even told about it when it was struck in August.

"They knew when they were stomping on my child's head that he was going to die. They should be accountable as adults," she said. "They made an adult choice."

The killers, Treavion Randolph, Dontral Beaver, Gianni Robinson - all now 17 years old - and Damien Hernandez, who has turned 18 since the attack, were charged in January.

Nevada can prosecute children as young as 13 for murder. However, those found guilty in the juvenile system in Clark County, which includes Las Vegas, can be kept in juvenile custody until they are 21.

They may be released earlier on parole if they complete rehabilitation programmes.

District Attorney Steve Wolfson defended the plea deal, saying it balanced the egregious facts of the case against potential legal challenges had it gone to trial.

Mr Wolfson added that the juvenile detention system would offer the killers more suitable resources for rehabilitation.

Jonathan was fatally injured on 1 November in an alley near Rancho High School. Footage posted on social media showed him taking off his shirt to prepare for a fight, reportedly over stolen headphones and a vape pen.

He was then swarmed by 10 students, pulled to the ground and beaten unconscious.

A member of the public found him and took him to back to the school, where staff attempted CPR before he was taken to hospital. He died six days later from a "non-survivable head trauma", police said.

Nine students, aged 13 to 17, were arrested over the attack.

Hernandez's lawyer Karen Connolly told CBS News: "Damien deeply regrets his participation in the melee which resulted in Jonathan's tragic death.

"He accepts full responsibility and will accept whatever punishment is meted out."