U.S. authorities look for militant links to shooters in California mass slaying

The couple suspected of killing 14 people at a holiday party in California amassed thousands of rounds of ammunition and a dozen pipe bombs, and authorities on Thursday sought to determine their motives and whether they had links to Islamist militants.

Syed Rizwan Farook, 28, and Tashfeen Malik, 27, his wife and mother of his 6-month-old daughter, were killed in a shootout with police five hours after Wednesday's massacre at the Inland Regional Centre social services agency in the city of San Bernardino.

Twenty-one people were wounded in the shooting, which ranks as the deadliest instance of U.S. gun violence in three years.

San Bernardino Police Chief Jarrod Burguan said at a Thursday news conference that the search of a townhouse leased by Farook and Malik in the nearby community of Redlands turned up flash drives, computers and cellphones.

Officials in Washington familiar with the investigation said so far there was no hard evidence of a direct connection between the shooters and any militant group abroad, but the electronics would be checked to see if the couple had been browsing on jihadist websites or social media.

CNN, citing law enforcement sources, said Farook had been "radicalised" and had been in touch through telephone and social media with more than one international terrorism suspect who was being investigated by the FBI.

USA Today, citing a federal law enforcement source, reported investigators were examining Farook's contacts with an undisclosed number of people whose suspected ties to radical ideology have become known to the FBI.

Officials from President Barack Obama to Police Chief Burguan said the attack may have been an act of terrorism but that questions of motive remained unanswered.

"It is possible that this was terrorist-related. But we don't know," Obama told reporters. "It is also possible that this was workplace-related."

Farook, a U.S. citizen, was born in Illinois, the son of Pakistani immigrants, according to Hussam Ayloush, who heads the Los Angeles area chapter of the Muslim advocacy group Council on American-Islamic Relations (CAIR).

David Bowdich, FBI assistant director in Los Angeles, said the couple had entered the United States in July 2014 after a trip abroad that included Pakistan and perhaps other countries.

He said Malik was admitted to the United State on a K-1 "fiancee visa" and was travelling on a Pakistani passport.

Farook, who according to public records worked as an health inspector for San Bernardino County, did not have a criminal record, Burguan said.

Police cited witness accounts that Farook had been attending the holiday party thrown for employees of the county Environmental Health Department but stormed out in anger. He then returned with Malik armed with assault gear and opened fire.

Burguan said they sprayed the room with 65 to 70 rounds.