Teen used 'ghost gun' in Saugus High School shooting, authorities in California say

LOS ANGELES — The teenager who opened fire last week on classmates at Santa Clarita's Saugus High School, fatally wounding two students before turning the gun on himself, used an untraceable "ghost gun" in the attack, Los Angeles County Sheriff Alex Villanueva said Thursday.

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Authorities said Nathaniel Tennosuke Berhow, 16, pulled a .45-caliber, 1911-model replica semi-automatic pistol from his backpack in the open-air quad at Saugus High School on Nov. 14. He shot five students at random, police said. Gracie Anne Muelberger, 15, and Dominic Blackwell, 14, were killed in the attack.

Investigators said Berhow saved the last bullet for himself. He died from a head wound the next day.

Authorities are working to determine who built the gun used in the attack, which included a partially built receiver, meaning it lacked a serial number, The Los Angeles Times reported.

"They're sold as a kit," Villanueva told KABC-TV. "You can legally buy it, assemble the weapon yourself and then you have a gun that is not registered, and no one knows that you have it. … That is very dangerous."

Authorities in Los Angeles have noted an increase in recent years in the use and proliferation of ghost guns. The guns are crafted from parts which require no background checks to purchase and so they lack serial numbers, officials with the Los Angeles Police Department and the Bureau of Alcohol, Tobacco, Firearms and Explosives said.

Officials with the ATF are assisting Los Angeles County sheriff's deputies as they work to trace the gun used by Berhow and several other registered and unregistered firearms seized last week from his home, according to KNBC and KCBS-TV. Six of the seized guns belonged to Berhow's late father, according to KCBS-TV.

The motive behind last week's shooting remained unclear Friday, despite a search of Berhow's home and police interviews with 45 people. Authorities said Berhow had shown no signs of violence and didn’t appear to be linked to any ideology or terrorist group. He ran cross country, was a Boy Scout and had a girlfriend.

Villanueva told KABC-TV that authorities were working to unlock Berhow's cellphone in an effort to gain more information.

The Associated Press contributed to this report.