Authorities on Saturday were investigating how a teenage boy gained access to a firearm and why he opened fire in the quad at Saugus High School, killing two students and wounding three others.
Parents had just dropped their teenagers off at school when the gun fire rang out Thursday morning, sending panicked students running out and others barricading in offices and classrooms.
The suspected shooter, identified as 16-year-old Nathaniel Berhow, appeared to fire randomly at the crowd for a few seconds before turning the gun on himself, authorities said. He died at a hospital Friday afternoon, sheriff's officials said.
Two of the five students shot, 15-year-old Gracie Anne Muehlberger and 14-year-old Dominic Blackwell, both died in the hospital on Thursday.
Berhow, a junior at the high school who authorities said carried out the attack on his 16th birthday, was described by officials and those who knew him as someone who wasn’t socially awkward or a loner. The teenager was a student athlete who was involved in school activities, the Sheriff's Department said.
"This is kind of out of the blue,” Los Angeles County Sheriff Alex Villanueva said.
A student at the school said Berhow always seemed happy, and never talked about having any issues.
"We thought everything was fine," Berhow's former teammate, Logan Marquez, told KTLA. "So when he goes out and does something like this, we were so confused and are trying to piece everything together. But we're coming up with nothing,"
Local authorities are working with the Bureau of Alcohol, Tobacco, Firearms and Explosives to analyze the weapon used in the shooting and trace its origin.
The agency traced six firearms registered to Berhow's father and all were accounted for, ATF Agent Carlos Canino said Friday. But at the teenager's home, investigators found several other guns, some not registered to the father and some not registered at all, according to Villanueva.
Investigators were still trying to determine whether the gun found at the scene is related to the firearms found at the home.
Villanueva said surveillance showed that the shooter appeared to be counting his rounds and knew exactly how many he had as he stood in the middle of the quad, firing at students.
“He seemed very familiar with firing the weapon,” the sheriff said. "... it wasn’t a spur of the moment act."
The firearm jammed at one point, but the teenager quickly cleared the malfunction and continued firing, according to the sheriff.
Authorities did not find a manifesto, diary or suicide note that would identify a motive, Capt. Kent Wegener of the Sheriff's Homicide Bureau said at a news conference Friday.
Two girls wounded in the shooting, ages 14 and 15, were expected to be discharged from the Providence Holy Cross Medical Center over the weekend. One had been shot in the left shoulder and lower right abdomen, and the other below the belly button, doctors said.
Saugus High School was expected to remain closed through the Thanksgiving break on Dec. 2, with optional programs offered to help students heal and process the trauma they've been through, Hart School District Deputy Superintendent Mike Kuhlman said in a written statement. All other schools within the district were scheduled to resume Monday.
KTLA's Sareen Habeshian contributed to this report.