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.

Herrera’s mother, Maggie Villard, said her son has missed many school days since learning about Lewis’ death. She said he left the house for the first time in over a week to come to the vigil.

“It took a lot to get him to come out, but I told him he needs closure, and this is a way to get that,” Villard said. “He did pretty good. I’m proud of him because he’s letting it all out.”

Information about the case initially was scant. The school held a moment of silence during morning announcements the day after the beating. Principal Darlin Delgado said in a staff meeting that she couldn’t go into detail about Lewis’ condition but that the police department’s homicide unit was investigating, D’Silva recalled.

The teachers gasped.

Detectives say Lewis walked to the alley with his friend after school but don’t believe he was the target. Police homicide Lt. Jason Johansson said cellphone video shows Lewis take off his shirt to prepare for the fight, then the 10 students “immediately swarm him, pull him to the ground and begin kicking, punching and stomping on him.”

After the fight, Johansson said, a person in the area found Lewis badly beaten and unconscious and carried him back to campus, where school staff called 911 and tried to help the student.

Barron, who has taught at the high school for nearly 30 years, said his colleagues who tried to help are “taking it really hard.” He said they didn’t leave Lewis’ side even after first responders arrived.

“You’re a dealer of hope if you’re a teacher,” Barron told the AP. “But this is something that really strikes the very core of who we are. We always hope our students will graduate and go on to lead productive lives. If we didn’t think so, I know I wouldn’t show up to work.”

On Tuesday night, friends of Lewis described him as a caring guy who kept to himself but spoke up when it mattered.

Students Andrew Cabrera and Luis Valenzuela said they weren’t surprised when they heard that Lewis had been standing up for a friend when he was attacked.

“That just sounded like him,” Cabrera said near the memorial site in the alley, where bouquets of flowers, candles and rose petals surrounded a stuffed animal with a signed note calling Lewis a hero.

It read: “Thank you for standing up for your beliefs.”