The attorney general of the District on Wednesday filed suit against one of the largest makers of parts for “ghost guns,” which when assembled have no serial number and cannot be traced. The suit claims that the guns cannot be legally marketed or sold to D.C. residents and that more than 83 percent of the ghost guns recovered in the city were made by Polymer80, the Nevada-based defendant in the suit.

Ghost guns are becoming an increasing problem for D.C. police, as they can’t be tracked to an original manufacturer or sales point. The number of ghost guns recovered in the city has risen from 25 in 2018, to 116 last year, to 106 in the first five months of this year, according to Attorney General Karl A. Racine (D). Racine said in a news release that Polymer80 handguns have been linked to nine homicides in the District since 2017.

David Borges, the CEO and co-founder of Polymer80, did not respond to a request for comment on the suit.

Manufacturers such as Polymer80 sell “gun assembly kits,” which often come with the lower 80 percent of the gun, and which the Bureau of Alcohol, Tobacco, Firearms and Explosives has ruled are not firearms when used as part of an AR-15 rifle. The other 20 percent, including the trigger and firing mechanism, can also be purchased online and, with some milling and assembly, can then be used to fashion a working handgun or rifle.

A ghost gun resembling an AR-15 rifle was used to shoot at two reserve police officers in Northeast Washington in December.

Racine launched the suit under the city’s Consumer Protection Procedures Act, saying Polymer80 falsely claims on its website that it can legally sell firearms in the District, that its firearms don’t need a serial number and that possession of its rifle receivers or handgun frames is legal.

“It is unlawful for a D.C. consumer to possess an unlicensed firearm in the District,” the lawsuit states, “including Defendant’s lower receivers and pistol frames.” The suit alleges that Polymer80′s sale of such parts to D.C. residents constitutes “unfair and deceptive trade practices prohibited by” the Consumer Protection Procedures Act.

Mark Oliva, a spokesman for the National Shooting Sports Foundation, the gun manufacturers’ trade association, has said that those who make illegal guns should be prosecuted but that building one’s own firearms is “a right protected under the Constitution.”