Untraceable, but legal, DIY "ghost gun" used in Saugus school shooting, police say

New details are also emerging about a deadly shooting earlier this week at a high school in California. The weapon used in the attack was a so-called "ghost gun," an untraceable, but legal weapon. 

Sixteen-year-old Nathaniel Berhow was too young to pass a background check or purchase a gun legally. Now it turns out the .45 caliber weapon he used to kill two of his high school classmates and wound three others was a homemade ghost gun.

"It was not registered to anybody," Los Angeles County Sheriff Alex Villanueva said. "We don't know the origins of the firearm, and that is a very big concern and a threat to public safety."

Ghost guns have been at the center of several high profile shootings, including last summer's death of a California Highway Patrol officer and a 2013 shooting spree in Santa Monica where five people were killed. These shootings both involved guns that were unregistered, untraceable and 100% legal to build. 

CBS News first reported on ghost guns in 2018. After going online, CBS News found all the parts needed to build one in a do-it-yourself kit. 

Retired LAPD SWAT officer Scott Reitz agreed to supervise CBS News' Carter Evans while he put all the components together. 

"It's not going to take a tremendous amount of gunsmithing skills," Reitz said.

It took just three hours while following an instructional YouTube video. Many of these videos are still online.

The Bureau of Alcohol, Tobacco, Firearms and Explosives showed CBS News several ghost guns taken off the streets. They now account for one-third of all guns seized in southern California, says the ATF's Ginger Colburn.

"These firearms are with gang members," Colburn said. "These firearms are being found at various crime scenes all over the country." 

"ATF can't go shut down the people who are selling these parts because these parts are not regulated," Colburn explained, when asked why the bureau doesn't put a stop to the sales of these kits. "It's really up to those companies to be responsible. They're the ones that are going to have to live with themselves...There's nothing the ATF can do."

There's no limit on the number of ghost guns one person can own, but a new California law now requires them to be voluntarily registered.

"It's really up to those companies to be responsible," Colburn said. "They're the ones who are going to have live with themselves." 

It's still unknown who made the gun used in the Saugus High School rampage. The answer may have only been known to the boy who carried out the attack on his 16th birthday and subsequently died by his own hand.