There's a hidden danger on the streets of Southern California that's skyrocketing in popularity among criminals — homemade ghost guns. They're untraceable.
They don't come with a serial number, you can build them at home and you don't need a background check to get them.
"If you can put Ikea furniture together you can make a gun at home," Carlos Canino, the special agent in charge of the Los Angeles Field Division of the Bureau of Alcohol, Tobacco Firearms and Explosives.
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Canino says nearly every day his agents are confiscating these homemade guns at an alarming rate.
"Thirty percent of the firearms that we're currently holding in our vaults are these unserialized homemade firearms," he said. "Before you used to see the AR-15 or .223 caliber rifle. Now, you're starting to see semi-automatic pistols."
Criminals who wouldn't otherwise be able to get a gun are flocking to them, according to Canino. A haul last year netted nearly 50 ghost guns off the streets from just one bust of a gang in Hollywood.
Investigators say they were going to be sold on the street. In 2013, police say a 23-year-old man used a ghost gun to kill two family members before going to Santa Monica college and taking the lives of three more people.
"It was barbaric the way they were killed," said Margaret Quinones-Perez, who lost her niece and her brother-in-law that day. "My loved ones died. Their blood was here on this campus. And the blood is going to be in every other parent that goes through it."
Investigators determined the killer tried to buy a gun legally, but couldn't pass a background check. So instead, he bought a kit online and assembled it himself.
"Where were the safeguards? Quinones-Perez said. "And then here I am five years later and there's no safeguards."
Experts say it's hard to police ghost guns. California law only regulates the finished product. But new legislation now requires anyone who assembles a homemade gun to register it with the California Department of Justice. Quinones-Perez will always be haunted by the violence.
"I still think about what would have been with Marci's life," Quinones-Perez said. "I think about that Carlos would have retired and he'd be with his wife. And his wife and his daughter wouldn't struggle as much as they do now."
The ATF says they have changed the way they conduct some of their investigations as ghost gun sales increase. Authorities acknowledge it is impossible to say how many are actually on the street, in the hands of people who shouldn't legally be allowed to have a gun.
The ATF says new technology, including 3D printing, is making it even easier for criminals to make these weapons.
The NBC4 I-Team worked with NBC Bay Area, NBC San Diego, and the nonprofit organization the Trace thetrace.org for this report.