A Southern California high school student killed two classmates and wounded three others on Thursday, pulling a .45 caliber semiautomatic handgun from his backpack and emptying it in a matter of seconds as the school day began.

He saved the last bullet for himself. It was his 16th birthday.

The teen gunman, whose name was not provided by police, survived the self-inflicted gunshot wound to the head but was in grave condition in hospital, law enforcement officials said.

Captain Kent Wegener of the Los Angeles County Sheriff’s Department told reporters the entire incident, captured on videotape, took 16 seconds as the young man stood in one spot and fired on one student after another.

“From right where he was standing, he doesn’t chase anybody, he fires from where he is until he shoots himself,” Wegener said.

The scene at Saugus High School was reminiscent of other mass shootings at US schools, including Marjory Stoneman Douglas High School in Parkland, Florida, where a former student with an assault gun killed 17 people on February 14, 2018.

It was the 85th incidence of gunfire at a school this year, according to Every town, a gun control advocacy group.

It seems sure to reignite a debate over gun control in the 2020 presidential election.

The two slain students were a 16-year-old girl and a 14-year-old boy. Two other girls, aged 14 and 15, were wounded, as was a 14-year old boy, Wegener said.

Investigators said they did not yet know what led the student to open fire at the school 65 km north of Los Angeles.

Police said the accused shooter had acted alone.

Investigators descended on his family home, blocking off the street. They found no further danger there.

A next-door neighbor, registered nurse Jared Axen, said the suspect had seemed introverted, quiet and sad, possibly despondent over the loss of his father from a heart attack in December 2017.

Axen, 33, said it was the boy who found his father deceased, not long after the older man had regained his sobriety and gotten his life “back on track” after years of struggling with alcohol abuse.

“I would say the boy was hurting and couldn’t ask for help,” Axen said of the suspect, who was a track athlete at the school, involved in Boy Scouts and liked the outdoors, going on hunting trips with his father.

He was of mixed race, born to Japanese-born mother and white father, with an older sister who became a nurse and moved away.

“I would ask him how school was, he would never bring up concerns of bullying or being a loner there,” Axen said.

There was no immediate word on where the teen gunman obtained the weapon.