San Bernardino shooting: Attackers 'modified weapons to make them more deadly'

The modified rifles violated Californian law

Weapons used by the suspects (San Bernardino County Sheriff's Department/ Facebook )

Modifications made to rifles used in a mass-shooting in San Bernardino made them more deadly and illegal under Californian law, authorities have confirmed.

The rifles were illegal to possess as they violated the state’s ban on assault weapons, the Bureau of Alcohol, Tobacco, Firearms and Explosives determined on Thursday.

Syed Rizwan Farook and Tashfeen Malik, left 14 people dead and 21 wounded when they stormed a Christmas party at the Inland Regional Center, carrying two .223-caliber semiautomatic weapons and two 9mm semiautomatic pistols, according to San Bernardino Police Chief Jarrod Burguan.

Meredith Davis, a ATF special agent, said the rifles were purchased legally with magazine locking devices – a gadget that fixes magazines into place, which can otherwise be detached for quick reloading, the Wall Street Journal reports.

Ammunition found inside the suspects' vehicle San Bernardino County Sheriff's Department (San Bernardino County Sheriff's Department/ Facebook)

The rifles had subsequently been altered in different ways to make them more powerful, Ms Davis said.

The .223 caliber rifle made by Smith & Wesson was changed to enable it to fire in fully automatic mode, while the other, a DPMS AR-15 model, was modified to use a large-capacity magazine.

California bans guns without magazine locking devices. Since 2000 the state has banned the sale or manufacture of magazines that can hold more than 10 rounds.

The state legally allows the sale and ownership of assault weapons that have fixed magazines.

Technicians will examine both rifles and an investigation remains ongoing over who purchased the weapons, Davis said.

Initial tests have suggested the modifications did not work, the Los Angeles Times reports.

The ATF confirmed the handguns used in the mass-shooting had not been modified and been purchased legally by Farook.

California approves the sale and use of certain handguns.

The weapons were found on Wednesday following a shootout in which both Farook and Malik were killed by police after fleeing the social services centre.

The suspect vehicle involved in a shootout with police San Bernardino County Sheriff's Department (San Bernardino County Sheriff's Department/ Facebook)

Authorities also recovered thousands of rounds of ammunition and explosive devices.

Under federal law, all fire arm purchases made through federally licensed dealers must be reviewed by the Federal Bureau of Investigation.

The review checks information such as whether the gun-buyer has a criminal history or has been involuntarily committed to a mental-health facility. However, background checks would not reveal other information such as whether a buyer has links to terrorism.