The FBI says it is investigating the deadly mass shooting in California as an ``act of terrorism.''
David Bowdich, assistant director of the FBI's Los Angeles office, made the declaration at a news conference Friday in California.
He also said the shooters attempted to destroy evidence, including crushing two cellphones and discarding them in a trash can.
He said authorities continue to investigate the case to understand the motivations of the shooters and whether they were planning more attacks.