Law enforcement officials are struggling with what they call an “astronomical” rise in untraceable ghost guns being sold online or on the streets. These firearms are illegal and oftentimes end up in the hands of criminals.

The issue comes after a joint operation by the San Mateo County Sheriff’s Office recovered 30 illegal firearms and arrested four men who were suspected of trafficking the weapons from Arizona.

The operation was part of the months-long investigation into illegal firearms led by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), the San Francisco Police Department and the San Francisco Drug Enforcement Administration Metro Task Force.

During the crackdown, police recovered automatic rifles, magazines and thousands of rounds of ammunition. In addition, authorities found a multitude of privately made ghost guns along with a 3D printer used for the manufacturing of these weapons.

Ghost guns have become a nationwide issue after having been used in a score of deadly shootings in the past five years. The homemade guns, usually in the form of handguns, have led to several states passing legislation barring ghost gun kits, as well as the removal of tutorial videos on social media sites.

Because they lack serial numbers, ghost guns are untraceable in law enforcement forensics databases, making it difficult to find potential criminals who use such weapons. In addition, ghost gun kits, which are often sold illegally, can be easily purchased over the internet without the need for a background check. The gun can then be assembled from the parts in the kit.

California law currently bans unserialized firearms, and requires homemade guns to have a serial number engraved on them within 10 days of manufacturing the weapon.

Experts say that despite regulations, the guns continue to be manufactured and distributed.

“It’s astronomical,” Mike Sena, executive director for the Northern California High Intensity Drug Trafficking Area and the Northern California Regional Intelligence Center, said. “Certain cities are only seeing a fraction of it, but when you look at the greater scale, especially in the western U.S., it’s just blown up.”

San Mateo County District Attorney Steve Wagstaffe estimated that round 30 to 40% of illegal firearms seized in the county were ghost guns.

In addition, South San Francisco police said that a quarter of all recovered guns in 2021 were ghost guns — 12 in total.

San Mateo County Sergeant Michael Leishman, who led the interstate trafficking operation, has witnessed firsthand the recent proliferation of ghost guns. “There’s definitely been a noticeable increase in crimes associated to ghost guns, such as robberies, shootings. From a seizure standpoint, I’ve definitely seen a significant increase in the seizure of PMFs (privately made firearms).”

Leishman said that when police recover ghost guns, there is no information for them to go off of to investigate their history or use in prior crimes.

“There’s no method of tracking records as far as the purchaser, the seller, the buyer,” he said. “It really hinders our ability to conduct a thorough investigation; it hinders our ability to track the life of that firearm.”

John Donohue, an economist and professor at Stanford Law School, said the ghost gun market is thriving in California due to the stricter gun regulations.

“One thing that struck me was in Texas, where it’s so easy to get guns by anyone, you don’t really have a ghost gun problem because you can pretty much walk into a store and get guns pretty easily. But in California, where it is harder to get guns lawfully, then you see the ghost gun market springing up.”

Wagstaffe also said that part of the difficulty in preventing the sale of ghost guns is because most of them are sold on the dark web or on the streets.

Still, there are some avenues for law enforcement to investigate and track the sale of ghost guns. Agencies are increasingly focusing their attention on social media platforms where manufacturers and sellers of ghost guns communicate.

“A lot of these individuals will use open source media or social media to communicate … and oftentimes we can use that as investigative leads,” Leishman said. “We’ll see certain patterns or images that catch our attention, and we’ll start digging further.”

Sena said one of his main goals as coordinator of the Western Region Crime Gun Intelligence Working Group (CGIWG) is to educate law enforcement on firearm laws and reporting ghost guns to understand the scope of the trafficking network.

According to Sena, the San Mateo County Sheriff’s Office actively collaborates with the CGIWG.

A spokesperson for the group said that Mateo County Sheriff Carlos Bolanos “is dedicated to supporting the Western CGIWG’s effort to combat illicit ghost guns with the combined resources of his crime lab, crime analysts and detectives.”

In addition to law enforcement efforts to combat the spread and use of ghost guns, lawmakers are also proposing legislation to ban ghost gun kits.

For instance, in 2016, San Francisco banned the sale and possession of ghost gun kits and parts, as well as their construction. Other cities are also following suit, as Oakland and Los Angeles recently proposed similar legislation.

On a federal level, the Biden administration is also working to propose legislation to regulate the sale of ghost gun kits and parts.

The bottom line is that ghost guns are likely to fall into the wrong hands, namely criminals or individuals who are not supposed to have access to guns in the first place. “It’s just another avenue for bad things to happen,” Donohue said.