SAN BERNARDINO, Calif. -- The husband-and-wife attackers who killed 14 people at a holiday party had enough bullets and bombs to slaughter hundreds more, investigators said Thursday as they worked to figure out whether the rampage was terrorism, a workplace grudge or some combination.
The couple left behind three rigged-together pipe bombs with a remote-control detonating device that apparently malfunctioned, and they had more than 1,600 unused bullets on hand when police shot and killed them in a rented SUV after an hours-long manhunt, police said.
At a family home, authorities also found 12 pipe bombs, tools for making more, and over 3,000 additional rounds of ammunition, Police Chief Jarrod Burguan said in a grim morning-after inventory that suggested Wednesday's bloodbath could have been far worse.
"We don't know if this was workplace rage or something larger or both," Attorney General Loretta Lynch said in Washington, echoing President Barack Obama. "At this point in time we don't know the motivation."
Wearing black tactical gear and wielding assault rifles, Syed Rizwan Farook, a 28-year-old county restaurant inspector, and his wife, Tashfeen Malik, 27, sprayed as many as 75 rounds into a room at a social service center for the disabled, where Farook's co-workers had gathered for a holiday banquet. Farook had attended the event but slipped out at some point, then returned in battle dress.
Four hours later and two miles away, the couple died in a furious gunbattle. They fired 76 rounds, while 23 law officers unleashed about 380, the police chief said.
Twenty-one people were injured before the day was out in this Southern California city of 214,000, including two police officers, authorities said. Two of the wounded remained in critical condition.
It was the nation's deadliest mass shooting since the Newtown, Connecticut, school tragedy three years ago that left 26 children and adults dead.
Authorities said the attack was carefully planned.
"There was obviously a mission here. We know that. We do not know why. We don't know if this was the intended target or if there was something that triggered him to do this immediately," David Bowdich, assistant director of the FBI's Los Angeles office, said as the bureau took over the investigation.
Farook has no known criminal record, Burguan said. He was born in Chicago to a Pakistani family, was raised in Southern California and worked at San Bernardino County's Department of Public Health for five years, according to authorities and acquaintances. The Saudi Embassy said he traveled to Saudi Arabia in the summer of 2014 for nine days.
As for Malik, she came to the U.S. in July 2014 on a Pakistani passport and a fiancée visa, authorities said.
Adam Lankford, a criminal justice professor at the University of Alabama, said his review of mass public shootings in the U.S. indicates this is the first one in recent history to involve a male-female team.
Federal authorities said that Farook legally bought two handguns used in the massacre and that their two assault rifles were legally bought by someone else. They did not say how the rifles got into the attackers' hands.
The stockpile of pipe bombs, tools and ammunition was found at a home in Redlands, about 7 miles from the massacre at the Inland Regional Center. Investigators said that Farook and his wife were listed on the rental agreement but that it wasn't yet clear whether they lived there.
Before they went on the rampage, couple dropped off their 6-month-old daughter with relatives Wednesday morning, saying they had a doctor's appointment, according to Hussam Ayloush, executive director of the Council on American-Islamic Relations.
Co-worker Patrick Baccari said he was sitting at the same banquet table as Farook before Farook suddenly disappeared, leaving his coat on his chair. Baccari said that when the shooting started, he took refuge in a bathroom and suffered minor wounds from shrapnel slicing through the wall.
The shooting lasted about five minutes, he said, and when he looked in the mirror he realized he was bleeding.
"If I hadn't been in the bathroom, I'd probably be laying dead on the floor," he said. Baccari said that up until then Farook showed no signs of unusual behavior and was a reserved young man.
The names of the dead were not immediately released.
Among the wounded was Julie Paez, who was at the holiday party. Paez, who tests water for the health department, was shot at least twice, and her pelvis was shattered by a bullet, according to her son, Nick Paez.
She managed to send her family a message through a group chat app to say she had been shot, and she included a selfie of just her face.
"It was a picture of her with a half-smile," her son said. "She just wanted to send us something so we would know what was happening."
Associated Press writers Brian Melley, John Antczak, Christopher Weber, John Rogers, Christine Armario and Sue Manning in Los Angeles; Amy Taxin and Kimberly Pierceall in Redlands; Eric Tucker, Tami Abdollah and Matthew Lee in Washington; Gillian Flaccus in Anaheim; Alina Hartounian in Phoenix; Michael Sisak in Philadelphia; and Hannah Cushman in Chicago contributed to this story. Pritchard reported from Los Angeles.