The couple suspected of killing 14 people at a holiday party in California amassed thousands of rounds of ammunition and a dozen pipe bombs, authorities say, as they sought clues to the pair's motives and whether they had links to Islamist militants.
Syed Rizwan Farook, 28, and his wife, Tashfeen Malik, 27, were killed in a shootout with police five hours after Wednesday's massacre at the Inland Regional Center social services agency in the city of San Bernardino, about 100km east of Los Angeles.
Twenty-one people were wounded in the attack.
The dead and wounded accounted for nearly half of the estimated 75 to 80 people who were in the room where the armed couple opened fire.
San Bernardino Police Chief Jarrod Burguan told a news conference the search of a townhouse leased by the two couple in the nearby community of Redlands turned up flash drives, computers and mobile phones.
Officials in Washington familiar with the investigation said there was no hard evidence of a direct connection between the couple and any militant group abroad, but the electronics would be checked to see if the suspects had been browsing on jihadist websites or social media.
One US government source told Reuters the FBI was examining information indicating that Farook was in contact with individuals who had themselves been under FBI investigation, some from cases already closed.
But no information has emerged suggesting any ties or contacts between Farook and the Islamic State or other specific militant groups, the source said.
Officials from President Barack Obama to Police Chief Burguan said the attack may have been motivated by extremist ideology 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 US citizen born in Illinois, was 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.
Malik, who had a six-month-old daughter with Farook, was a Pakistani native living in Saudi Arabia when they married, Ayloush said.
David Bowdich, FBI assistant director in Los Angeles, said Malik was admitted to the US on a K-1 "fiancee visa" and was travelling on a Pakistani passport.
The couple entered the US in July 2014 after a trip that included Pakistan, Bowdich said. Farook also visited Saudi Arabia for nine days in the (northern) summer of 2014, the kingdom's embassy said.
The director of the Islamic Center of Riverside, a mosque Farook attended regularly for two years, described him as a devout Muslim who made the pilgrimage to Mecca in Saudi Arabia a few years ago and celebrated his wedding reception at the mosque.
Farook, who according to Burguan had no criminal record, worked as an inspector for San Bernardino County Department of Environmental Health, the agency throwing the holiday party that came under attack.
Police cited witness accounts that Farook had been attending the celebration but stormed off in anger, then returned with Malik armed with assault gear and opened fire. Burguan said they sprayed the room with 65 to 70 rounds.
Burguan said the couple had two assault-style rifles, two semi-automatic handguns and 1600 rounds of ammunition in their rented sport utility vehicle, when they were killed.
At the townhouse, police found another 4500 rounds, 12 pipe bombs and bomb-making equipment. One bomb was rigged to a remote-control device.
As the FBI-led investigation pressed on Thursday, authorities completed formally notifying the families of the 14 people who died and made their names public.
The victims, all from Southern California, ranged in age from 26 to 60, and most were men, according to the county coroner. All but two of the dead and three of the wounded were county employees.
About 200 worshippers gathered on Thursday night at the Ahmadiyya Muslim Community mosque, San Bernardino's largest, to hold a vigil for victims of the shooting.
Meanwhile, a larger, more diverse crowd estimated by police at about 3500 packed the San Manuel Stadium, a municipal baseball park downtown, for a candlelight memorial.
