President Barack Obama said it's possible the mass shooting in San Bernardino, California, was related to terrorism, but that authorities still don't know at this stage of the investigation. He said it's possible it was workplace-related or that there "may be mixed motives."
"There may be mixed motives in this, which makes the investigation more complicated," Obama said.
He said the FBI is now in charge of the investigation in cooperation with local law enforcement.
He's assured Americans that authorities will get to the bottom of why the rampage occurred. Obama also called for people to wait for facts before making judgments.
Obama said many Americans feel there's nothing they can do about mass violence, but "we can't just leave it to our professionals to deal with the problems of these horrible killings," he said. "We all have a part to play."
The president acknowledged that gun violence can't be eliminated completely but that it's possible to make it harder for people to carry out such violence.
"When someone wants to do harm to others, we want to make it harder," Obama said. "Because it's too easy right now."
Obama has ordered U.S. flags to be flown at half-staff to honor the victims of the shooting. The White House said Obama signed the proclamation Thursday. It calls for flags to remain at half-staff through Monday and affects flags at the White House, public buildings, military installations, U.S. Navy ships, embassies and diplomatic missions.
Obama said in an interview with CBS News on Wednesday that the latest deadly rampage reminded him of a pattern of mass shootings he said "has no parallel anywhere else in the world."
According to ShootingTracker.com, which tracks deaths by guns in America, the U.S. has seen 355 mass shootings — defined as incidents in which four or more victims are shot — so far in 2015.
Obama told CBS that some measures could quickly be taken to curtail the frequency of mass shootings in the U.S.: "Common sense gun safety laws, stronger background checks" and preventing people who are on the no-fly list from buying firearms, because now "there's nothing we can do to stop them."
Police said Syed Rizwan Farook, 28, and his wife, Tashfeen Malik, 27, slaughtered 14 people and seriously wounded 21 others in an attack Wednesday at a social service center for the disabled before they were killed in a shootout with police four hours later.
Police said Thursday the couple had left behind a remote controlled explosive device that failed to detonate at the holiday party, and 12 pipe bombs and other arsenal were recovered at the couple's home, police said Thursday.
Investigators were still trying to determine why the couple left their baby daughter behind and and went on the rampage — the nation's deadliest mass shooting since the Newtown, Connecticut, school tragedy three years ago that left 26 dead.
Authorities told NBC News that Farook appeared to have been radicalized. They said he had been in touch with people in the Los Angeles area who have expressed jihadist-oriented views and he appeared to have been in some form of communication with overseas individuals who are persons of interest to American authorities.