Los Angeles County Sheriff's Detective Daniel Finn, Inglewood police Officer Sean Yanez and Los Angeles police Officer Gus Ramirez were dropping off their children Thursday morning at the Santa Clarita school when they saw scores of children rushing off campus.
Finn said he was taking his girlfriend's son to Saugus High when he saw "several hundred" students fleeing. He got out of his vehicle and stopped a teenager, who said students heard gunfire on campus.
The detective and officers immediately ran toward the sound of the gunshots and within moments found several students, including the gunman, in the quad area suffering from gunshot wounds from the 16-second shooting.
Finn was the first to arrive at the scene, where he saw the .45 caliber semi-automatic gun and determined it was safe enough to begin providing first-aid, Villanueva said.
"My main concern then was securing the scene, treating the victims and trying to make sure there was an additional shooter on campus," Finn said at a news conference Friday.
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Two teenagers were killed in the shooting and three others were wounded. The gunman, only identified by authorities as a 16-year-old Saugus High junior, was hospitalized in grave condition with a self-inflicted gunshot wound, authorities said.
The gun was not found directly next to the shooter, making it difficult to determine who the gunman was, according to Finn.
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Deputy James Callahan, a school resource officer at Saugus High, said he was already heading to the school when the shooting was reported and responded within minutes. He coordinated with the off-duty deputy and officers to provide medical aid.
"When you're a school resource deputy, you take a lot of pride in keeping your campus secure and you never think a tragic thing like this is going to happen," Callahan said.
Villanueva praised the officers for their heroism.
"What they did yesterday was extraordinary," he said. "Their actions definitely saved lives and my hats off to them."
Hospital doctors said Friday two teenage girls wounded in the shooting were recovering and could leave the hospital soon. A third surviving victims, described as a 14-year-old boy, was released from Henry Mayo Newhall Hospital Thursday.
Investigators searched the gunman's home as they sought a motive for the attack, which seemed to target students at random, Los Angeles County Sheriff's Department Captain Kent Wegener said. Several guns were found in the home, though it is unclear who the firearms belong to.
The Associated Press contributed to this story.