LAS VEGAS (AP) — Students at a Las Vegas high school had gone home for the day when an urgent message was broadcast from the intercom: A defibrillator was needed near one of the classrooms.

A nurse ran in the direction of the emergency. A group of teachers tried to perform CPR. It wasn’t until the next day that social studies teacher Reuben D’Silva learned what happened — a student who was standing up for a friend was put on life support after being brutally beaten by 10 of his peers in a nearby alley.

It was a devastating episode for Rancho High School, a predominantly minority campus in east Las Vegas. Some students walked out of class when they heard Jonathan Lewis Jr., 17, wouldn’t survive head trauma and other injuries he suffered in the Nov. 1 attack, D’Silva said.

Adding to the devastation is that cellphone video of the beating was widely shared across social media.

In the following weeks, a small memorial sprung up in the trash-littered alley bordered by apartment buildings and a sober living home. Students, teachers and staff were left to grapple with how a conflict over a stolen vape pen and a pair of wireless headphones escalated.

“The trauma, quite frankly, extends beyond the young man’s family,” said psychology teacher Isaac Barron, a councilman in neighboring North Las Vegas. “It’s going to run deep, and there’s no magic wand to solve this.”

At least eight of the 10 teenage students who police believe took part in the attack have been arrested. Four were formally charged Tuesday as adults with second-degree murder while the other students await separate hearings because they are under 16.

A room on campus was set up with social workers and counselors to hear students and staff in their grief. That’s where D’Silva, himself a graduate of Rancho, sent his students when they learned their classmate was being taken off life support.

“It’s so difficult to grapple with something like this, where you have a fight that just turns into a brutal beatdown of a student by other Rancho students,” D’Silva told The Associated Press. “Everybody at Rancho either knew the victim or the perpetrators — or both.”

At a vigil Tuesday night in the alleyway, dozens gathered to remember Lewis, placing long-stemmed white roses in the spot where police say he was attacked. A school photo of the teen placed on a table with candles looked back at the crowd.

As the group thinned, Lewis’ mother, Mellisa Ready, was standing near the stack of roses and crying when 16-year-old Arturo Herrera approached. Herrera, gulping back tears, said he was a friend of her son.

Ready, who did not speak during the vigil, pulled Herrera in for a hug, the two crying into each other’s shoulders.