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The Latest: 4 guns used in California shooting were purchased legally, 1 buyer investigated

  • Law enforcement search for a suspect in a mass shooting that occurred at a Southern California social services center on Wednesday, Dec. 2, 2015, in San Bernardino, Calif. One or more gunmen opened fire Wednesday at a California center that serves people with developmental disabilities, shooting several people as others locked themselves in their offices, desperately waiting to be rescued by police, witnesses and authorities said. (AP Photo/Chris Carlson))

    Law enforcement search for a suspect in a mass shooting that occurred at a Southern California social services center on Wednesday, Dec. 2, 2015, in San Bernardino, Calif. One or more gunmen opened fire Wednesday at a California center that serves people with developmental disabilities, shooting several people as others locked themselves in their offices, desperately waiting to be rescued by police, witnesses and authorities said. (AP Photo/Chris Carlson))  (The Associated Press)

  • In this image taken from video, armored vehicles surround an SUV following a shootout in San Bernardino, Calif., Wednesday, Dec. 2, 2015. The scene followed a military-style attack that killed multiple people and wounded others at a California center that serves people with developmental disabilities, authorities said.   (KTTV via AP)

    In this image taken from video, armored vehicles surround an SUV following a shootout in San Bernardino, Calif., Wednesday, Dec. 2, 2015. The scene followed a military-style attack that killed multiple people and wounded others at a California center that serves people with developmental disabilities, authorities said. (KTTV via AP)  (The Associated Press)

  • Law enforcement search for a suspect in a mass shooting that occurred at a Southern California social services center on Wednesday, Dec. 2, 2015, in San Bernardino, Calif. One or more gunmen opened fire Wednesday at a California center that serves people with developmental disabilities, shooting several people as others locked themselves in their offices, desperately waiting to be rescued by police, witnesses and authorities said. (AP Photo/Chris Carlson)

    Law enforcement search for a suspect in a mass shooting that occurred at a Southern California social services center on Wednesday, Dec. 2, 2015, in San Bernardino, Calif. One or more gunmen opened fire Wednesday at a California center that serves people with developmental disabilities, shooting several people as others locked themselves in their offices, desperately waiting to be rescued by police, witnesses and authorities said. (AP Photo/Chris Carlson)  (The Associated Press)

The latest on the mass shooting at a social services facility in San Bernardino, California (all times local):

3 a.m.

Federal authorities say that the two assault rifles and two handguns used in the San Bernardino massacre were all purchased legally in the United States — two of them by someone who's now under investigation.

Meredith Davis of the Bureau of Alcohol, Tobacco, Firearms & Explosives says investigators are now working to make a connection to the last legal purchaser.

She says all four guns were bought four years ago but she's not saying whether they were purchased out of state or how and when they got into the hands of the two shooters.

Davis says California requires paperwork when guns change hands privately but many other states don't.

She also says the rifles involved were .223-caliber — powerful enough to pierce the standard protective vest worn by police officers, and some types of ammo can even plow through walls.