Los Angeles street gangs are building their own AR-15-style rifles and other guns, known as “ghost guns” because they are untraceable, according to new evidence revealed by the LAPD and federal firearms agents.

At a press conference Thursday at LAPD Hollywood Division, Hollywood-area detectives and the ATF (Bureau of Alcohol, Tobacco, and Firearms) revealed the results of a six-month investigation that included home-made weapons. “This is a trend among Southern California gangs, what that means is, criminals are making weapons because they cannot buy them legally,” the ATF agent in charge said.

Ten arrests were made in the seizure; the ghost guns were laid out on a table, half of which appeared to be semi-automatics. They also included an AK-47 and an SKS, Russian military assault rifles.

Gang members are barred from legally purchasing weapons and have increasingly started to manufacture their own from unfinished kits used in AR-15 manufacturing, explained ATF Special Agent Bill McMullan in a statement.

“Search warrants at the end of the investigation resulted in the seizing of firearms manufacturing tools and materials used to build AR-style rifles and pistols from unfinished lower receiver kits, McMullan said.

The joint task force said it conducted more than a dozen undercover operations focusing on ghost guns between January and June of 2018. Ghost guns are made without serial numbers and sold without background checks.

The LAPD said, its detectives often recover ghost guns when investigating crimes in the city. “Los Angeles has seen an increase in the number of ‘ghost guns’, particularly in the form of semi-automatic 9mm pistols.”

A total of 47 felony counts related to the manufacturing and sales of ghost guns were filed with by the Los Angeles District Attorney.