Police are still searching for a motive in the shooting at a Southern California high school Thursday morning.
Authorities have conducted more than 40 interviews but have not uncovered a manifesto, diary, suicide note or writings, Capt. Kent Wegener of the Los Angeles County Sheriff's Office said at a press conference Friday afternoon.
The suspect, identified Friday as Nathaniel Tennosuke Berhow, fatally shot two classmates and injured three others before shooting himself in the head with his last bullet during the 16-second attack Thursday morning, said Los Angeles County Sheriff Alex Villanueva.
Berhow died about 3:30 p.m. PDT at a hospital.
Students who recently filmed an active shooting training video said they couldn't believe violence struck at Saugus High School in Santa Clarita, home to Six Flags Magic Mountain and 30 miles northwest of downtown Los Angeles.
The incident was the 30th shooting attack at a school this year, according to the gun safety group Everytown.
Here's what we know so far:
What happened at Saugus High School?
The gunman pulled a weapon out of his backpack around 7:30 a.m. local time and opened fire at the school, which has a student population of about 2,500 in grades 9-12.
He shot five students in the quad area with a 45-caliber semi-automatic handgun before shooting himself, said Capt. Kent Wegener of the Los Angeles County Sheriff's Office.
L.A. County Sheriff Alex Villanueva said Friday that surveillance footage showed the shooter entering the quad, taking out a pistol from his backpack and firing the first round.
The gun then apparently jammed, Villanueva said, and the shooter was forced to take time to fix it before firing a second round and then injuring the remaining four students. Then, he used the last round on himself.
According to Villanueva, the entire incident happened over 16 seconds. The shooter "seemed very familiar with the weapon," and his exact knowledge of how many rounds were in the gun suggests that the shooting "wasn't a spur of the moment act," Villanueva said.
The sheriff dismissed suggestions Friday that the shooter had targeted his ex-girlfriend. "As far as we know, the actual targets were at random," Villanueva said.
The shooter's mother had dropped him off at school that morning, Villanueva said.
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Saugus and all other schools in the district went on lockdown as police swarmed the area. Once students were allowed to reunite with their parents, families were seen embracing and crying.
The school district remained closed Friday. Counselors at a local church comforted parents and students. Santa Clarita Mayor Marsha McLean said that the city would be launching a website Friday at saugustrong.org to provide resources to the community. A vigil was planned for Sunday.
Who is the suspect?
Officials described Berhow as an Asian male student at the school whose 16th birthday was Thursday.
Neighbors and classmates described him as pleasant but noted that he was changed by the death of his father two years ago.
The suspect was a quiet, normal student, said Brooke Risley, a 16-year-old junior. He ran cross country and was a Boy Scout.
"He doesn't seem like the kind of kid to do this," Risley said.
Though the teen was sometimes a little sad, next-door neighbor Jared Axen said he didn't come off as depressed.
Berhow's father died from a heart attack in December 2017, according to an obituary. Although his father had owned guns, Axen, 33, said he didn't think Nathaniel Berhow viewed them in an unhealthy way.
Who are the victims?
They're all students. A 16-year-old girl and a 14-year-old boy died at a local hospital. Wegener said the three injured victims are two girls, 14 and 15, and a 14-year-old boy. None of the victims have been identified by law enforcement.
Officials on Friday released the identity of one victim, Gracie Anne Muehlberger, 15, who succumbed to her injuries Thursday morning with her parents by her side. The other victim who died was identified as 14-year-old Dominic Blackwell.
The two girls are in good condition and the boy was discharged Thursday, according to officials at Henry Mayo Newhall Hospital and Providence Holy Cross Medical Center.
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The two girls taken to Providence Holy Cross Medical Center were "sitting up, smiling, and talking" by Friday morning, doctors at said in a press conference.
The 15-year-old girl underwent surgery, and doctors expected to discharged her within the next two days. The 14-year-old girl, who sustained superficial injuries, was expected to be discharged soon.
The doctors commended the girls' composure throughout the process. "These are historic young adults," said Dr. Boris Borazjani. "They held their composure despite being shot, and being shot in the torso is a big deal."
Doctors said that the victims were working through the "profound psychological effect" of the incident, and that they would be receiving support and counseling from professionals at the hospital.
Other than attending the same school, Wegener said law enforcement officials have not found a relationship between the shooter and the victims. The two girls at Providence Holy Cross Medical Center appeared to know each other, doctors said Friday, but they could not say if the girls were familiar with the suspected shooter.
How did the suspect get a gun?
Authorities on Friday were still analyzing the weapon and its origin, Wegener said.
Law enforcement officials have not shared any information about how the suspected shooter obtained the gun used in Thursday's assault. The 16-year-old couldn't have legally bought it himself: In California, licensed dealers cannot sell a firearm to anyone under age 21.
Authorities said that they had recovered several firearms from the shooter's home and had accounted for all firearms registered to the shooter's father. Some of the firearms recovered from the home, however, were not registered to the father, and some were not registered at all, Villanueva said.
Were there any warning signs?
Authorities said Friday that they were still working to identify any social media accounts linked to the shooter. A post on an Instagram account that said "Saugus, have fun at school tomorrow" was not linked to the shooter but originated outside of the country, Wegener said.
"We disabled this account for violating our policies," an Instagram spokesperson confirmed to USA TODAY via email. "We can confirm it did not belong to the shooter."
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Wegener said his department looked into recent threats against Saugus High and identified two, both of which were investigated and deemed to be unrelated to Thursday's shooting. Authorities have not determined a motive but don't believe he was acting on any ideology.
What safety measures were in place?
The school district website says a resource officer is assigned to every campus, and the schools have fencing and supervisors monitoring who goes in and out. The Saugus High campus is fenced and has a dozen security cameras but no metal detectors.
"The gates to the campuses are locked during instructional time and typically only unlocked when students are leaving campus for lunch or leaving school at the end of the day. Visitors are directed to the office to check-in.''
Contributing: Jorge Ortiz and Mike James, USA TODAY
This article originally appeared on USA TODAY: Santa Clarita shooting: Saugus High School closed; what we know now