Modifications made to rifles used Wednesday in the mass shooting in San Bernardino made them technically illegal to possess in California under the state's assault weapons ban.
Fourteen people died and 19 people were injured in the shooting at the Inland Regional Center. Two police officers were later injured during a shootout that killed suspects Syed Farook and Tashfeen Malik.
Meredith Davis, a special agent with the bureau of Alcohol Tobacco and Firearms, said the rifles were purchased legally. But the .223 caliber Smith & Wesson M&P 15 authorities recovered had been modified to make it fully automatic, illegal under federal law.
A field test of the rifle showed the modification did not work, she said.
The other rifle - a .223 caliber DPMS A-15 - was modified to accept a high-capacity magazine, and to bypass the so-called bullet button, which makes removing a magazine easier, Davis said.
California bans guns with magazines that detach for quick reloading. Since 2000 the state has banned the sale or manufacture of magazines that can hold more than 10 rounds.
At least four magazines designed to hold 30 rounds were recovered from the Inland Regional Center.
Technicians are coming to California to examine both rifles to make an official determination, Davis said.
Davis said the agency isn't publicizing where the rifles were sold, and declined to name the person who purchased the rifles citing the ongoing investigation.
Earlier Friday, the Dave Bowdich, the FBI’s assistant director in charge of the Los Angeles Field Office, said the agency has spoken to the person who purchased the rifles. "That person is not under arrest at this point," Bowdich said.
The rifles and two semi-automatic handguns were found Wednesday following the shootout. The handguns recovered had not been modified, Davis said. Authorities said Farook purchased those firearms legally.
Authorities also recovered thousands of rounds of ammunition, explosive devices and a .22 caliber rifle.
Legislators enacted California's assault weapons ban in 1989. Following a court challenge in 2000, the law was upheld. Gun owners could keep their assault weapons provided they registered with the state before Jan. 23, 2001.
There are some 145,000 assault weapons that remain in the state under this grandfather provision, according to state Department of Justice data.