SAN FRANCISCO (CBS SF) — The state of California is jumping into an historic lawsuit against companies who make kits to assemble so-called “ghost guns.”

The suit, originally filed in August by the San Francisco District Attorney’s Office along with the Giffords Law Center to Prevent Gun Violence and the law firm Keker, Van Nest & Peters, accuses three companies of selling illegal prepackaged kits, allowing people to make a firearm at home. These ghost guns don’t have serial numbers, making them untraceable.

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The joint effort announced Wednesday will strengthen a lawsuit filed against three gun manufacturers by the District Attorney Chesa Boudin in August.

The lawsuit alleges the companies Glockstore, Blackhawk, and MDX Performance violated state laws that require them to apply for serial numbers and that they misled consumers into believing the weapons were legal.

In joining the lawsuit against Blackhawk Manufacturing Group, Inc., GS Performance, LLC, and MDX Corporation, California Attorney General Rob Bonta said the defendants are violating the federal Gun Control Act and two state gun control measures by not meeting basic safety requirements.

“Fifteen minutes — that’s the little time it takes to put it together. We’re not talking about a kit of Legos, we’re not talking about Blue Apron or Martha Stewart’s meal kit, and we’re not talking about a COVID test. We’re talking about a ghost gun kit,” said Bonta. “These weapons have been used in mass shootings. Criminals have used them to murder innocent children in our classrooms. They have been linked to serious crimes here in San Francisco and across the nation. And in America, we have a gun problem. We have to acknowledge that.”

According to the San Francisco Police Department, nearly half of the firearms recovered in 2020 in connection with homicides were ghost guns; in 2019, that number was just 6%.

Because of the nature of the product, ghost gun kit manufacturers do not follow firearm sales regulations. The kits are also easy to assemble — several YouTube videos and websites are available to help buyers.

“Gun kits sold by each of these three retailers can be used to self-assemble deadly, un-serialized, largely-untraceable guns that fail to meet California firearm safety standards, allowing anyone — from terrorists to human traffickers — to bypass California’s nation-leading gun laws, including registration and background checks,” said Bonta. “Within minutes, they will have an instrument of death in their hands.”

District Attorney Chesa Boudin said ghost gun companies deceive California consumers into believing that ghost guns are legal, thus engaging in false advertising and fraudulent business practices.”

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“We know that in this day and age that there is nothing that presents a greater threat to public safety than guns — specifically unserialized ghost guns that are being dumped into our communities and into the hands of people who are prohibited from possessing firearms,” said Boudin. “People who intend to use those firearms to commit crimes. Whose very possession of those firearms is a crime.”

KPIX has been investigating ghost guns for years, investigating how easy it is to illegally alter and assemble parts without serial numbers.

“There are people who are buying these kits for the purpose of assembling them, finishing them and then selling them to the highest bidder. That’s a big problem,” said ATF Special Agent Graham Barlow in an interview in 2019.

Building an unserialized firearm out of parts for personal use is legal under federal law. But selling it is not.

California has some of the strictest gun laws in the country. But in 2020, the state accounted for 65% of all ghost guns seized by the ATF according to state and city officials.

Mattie Scott’s son was shot and killed decades ago.

“Ghost Guns have magnified the problem as we have seen in Oakland 102 mothers and fathers will be going to the cemetery instead of graduation,” said Scott.

The lawsuit seeks monetary penalties and an injunction prohibiting defendants from violating federal and state gun laws. There has been no comment from the defendants as of Wednesday afternoon.

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Kenny Choi contributed to this story.