SANTA CLARITA (CBSLA) — All schools in the William S. Hart Unified School District were closed Friday, a day after a shooting left two Saugus High School students dead and the 16-year-old gunman in grave condition from a self-inflicted gunshot wound.

Investigators say surveillance video showed Nathan Berhow, who turned 16 on Thursday, marked his birthday by walking into the quad of Saugus High School, pulled a gun out of his backpack, shot five people around him, then turned the gun on himself – all within 16 seconds.

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Gracie Anne Muehlberger (credit: CBS)

Gracie Anne Muehlberger, 15, was identified Friday as one of the two students who died of their gunshot wounds.

Dominic Blackwell, 14, was later identified as the other student fatally wounded.

The three other students who were wounded are in stable condition, according to Mike Kuhlman, deputy superintendent of William S. Hart Unified School District.

Berhow, who was identified as the shooter by CBS News, remains in critical condition. He was also a student at the school.

Student Micah Turner was a witness to the shooting.

“He was wearing black sunglasses at the time. He looked very familiar. Then he shot two people,” she said. “I just saw him fire one, two, three … then I knew I had to get out of here. Like, we looked at each other.”

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Dominic Blackwell (credit: CBSLA)

Authorities have not identified a motive in the shooting.

“As far as we know, the actual targets were at random,” Los Angeles Sheriff Alex Villanueva said at a Friday afternoon news conference. “There’s no relationship we can tell with the suspect and the victims.”

Investigators are also unsure how he obtained the .45 caliber pistol that was used in the killings or who it belonged to. Villanueva said that six firearms found at Berhow’s home were registered to his late father. The gun used in the shooting was not one of them, Villanueva said. There were several more guns found in the home which were unregistered.

“There were several firearms recovered from the house,” Villanueva said. “We’ve accounted for all of the firearms that were registered to the father. Beyond that we’re gonna have to go through and finish the investigation to account for all the firearms and match them up with the source and the relationship with the weapon we recovered at the scene.”

“Some of these firearms were not registered at all,” Villanueva added.

The Bureau of Alcohol, Tobacco, Firearms and Explosives is assisting with that investigation into the origin of the gun.

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Meanwhile, all schools in the district were closed Friday. Grief counselors are being provided to students and staff at Grace Baptist Church, 22833 Copper Hill Dr.