Santa Clarita - California police on Friday were working to identify what motivated a 16-year-old to open fire on his fellow high school students a day earlier, killing two and wounding three others before shooting himself in the head.
Detectives worked through the night to follow up on tips related to Thursday morning's attack at Saugus High School in Santa Clarita, about 40 miles (65 km) north of Los Angeles. The shooting, which was caught on video, unfolded in 16 seconds, the Los Angeles County Sheriff's office said.
Arriving at school on his 16th birthday, the suspect pulled a .45 semi-automatic pistol from his backpack in an outdoor school courtyard, stood in one place and shot his victims in rapid succession before turning the gun and firing the last bullet into his head.
Sheriff Alex Villanueva of the Los Angeles County Sheriff's Office said on Friday that the suspect's motive was the question of the day.
"This kind of came out of the blue," the sheriff told CNN. "It shocked everyone who knew him."
All Hart District schools in Santa Clarita were closed on Friday, the Santa Clarita Valley Sheriff's office said on Twitter, out of respect for the victims and their families.
Police said on Thursday that investigators were interviewing the mother and girlfriend of the suspect, whose name they have not released, and are looking for clues about his motive on social media. They believe he acted alone.
The gunman survived the self-inflicted gunshot wound but was in grave condition in a hospital, officials said.
The FBI is assisting in the investigation and police do not know yet where the suspect got the weapon, Villanueva said.
Investigators descended on his family home, about 2 miles (3.2 km) from the high school, immediately after responding to the scene at the school and found no further danger there.
Two girls aged 14 and 15 were being treated at Providence Holy Cross Medical Center in Mission Hills, California and were listed in good and fair condition, a hospital spokeswoman said early on Friday.
At the Henry Mayo Hospital in Santa Clarita, authorities said a 14-year-old boy was treated and released. Two other students who had been taken there died. A hospital spokesman could not immediately be reached on Friday.
The names of the wounded and dead have not been released, but the county sheriff said the two slain students were a 16-year-old girl and a 14-year-old boy.
The scene at Saugus High School was reminiscent of other mass shootings at U.S. schools, including Marjory Stoneman Douglas High School in Parkland, Florida, where a former student with an assault rifle killed 17 people on Feb. 14, 2018.
It was the 85th incident of gunfire at a school this year, according to Everytown, a gun control advocacy group.