Was there a connection to terrorist groups? Law enforcement sources say Farook had been in contact with more than one person who had been the subject of an international terrorism investigation by the FBI.
Farook was a U.S. citizen and an environmental health specialist for San Bernardino County. He had worked there for five years.
He graduated from California State University, San Bernardino, with a degree in environmental health in 2010, school spokesman Joe Gutierrez said. Farook had a profile set up on iMilap.com, which describes itself as "a site for people with disabilities and second marriage."
The profile said he "enjoys working on vintage and modern cars, reads religious books, enjoys eating out sometimes."
"Enjoys traveling and just hanging out in the backyard doing target practice with his younger sister and friends."
Malik was a native of Pakistan who came to the United States on a "fiancee visa" and later became a lawful permanent resident. The couple had a 6-month-old daughter.
On Thursday, law enforcement officials said Farook was in touch over the phone and via social media with more than one person who had been the subject of an FBI international terrorism investigation. It appears that he was radicalized, which contributed to his motive, though workplace grievances might have also played a role, other law enforcement sources said.
President Barack Obama hinted as much when he said that the attackers may have had "mixed motives."
Farook had traveled to Pakistan, according to David Bowdich from the FBI's Los Angeles office. And he'd also gone to Saudi Arabia in 2013 for the Hajj
, the pilgrimage to Mecca that Muslims are required to make at least once in their lifetimes, law enforcement officials said.
That's where and when he met Malik.
Saudi and U.S. officials said records show Farook also was in Saudi Arabia in July 2014. He was there for nine days, a Saudi official said. A U.S. official described the 2014 trip as Farook's "last recorded" trip to the country.
On Wednesday, the couple left their daughter with Farook's grandmother, saying they had a doctor's appointment, according to Hussam Ayloush, the head of the Southern California chapter of the Council on American-Islamic Relations.
Farook attended the holiday party at the Inland Regional Center in San Bernardino, California. It's a facility for people with developmental disabilities.
Farook abruptly left the center before the shooting "under circumstances described as angry," said San Bernardino Police Chief Jarrod Burguan.
About 11 a.m. local time, Farook came back with Malik. They wore tactical gear that allowed them to carry items such as ammunition, but they weren't wearing protective armor, Burguan aid. They carried rifles and semi-automatic handguns.
They fired 65 to 75 rounds, police said, killing at least 14 people and wounding at least 21.
The couple then escaped in a dark-colored, rented Ford SUV with Utah plates.
Acting on a lead about where Farook lived, authorities went to a home in Redlands, about 10 miles from San Bernardino, to serve a search warrant.
While they were there, the black SUV passed by slowly, then sped up and raced off, a law enforcement official close to the investigation said.
A police cruiser pursued it.
The chase ended back in San Bernardino, about two miles from Inland Regional. Farook fired at officers from the vehicle while Malik drove, officials said.
The couple fired about 76 rounds total at pursuing officers, police said. Twenty-three officers returned fire with about 380 rounds, police said. Farook and Malik were killed.
Police detained one man who was seen running away after the shootout. Authorities determined that he had nothing to do with the shooting, though he did happen to have an unrelated misdemeanor warrant out on him, Burguan said.
The shooters had more than 1,400 rounds of .223-caliber ammunition and more than 200 9mm rounds on their person or in their vehicle, Burguan said.
Two of the firearms have been traced back to them; they were purchased legally. Two rifles were purchased -- also legally -- by someone else, possibly a roommate, an official said. Authorities don't think that person had anything to do with the attack.
A bag believed to belong to the shooters was found in the conference room where the party was held. Inside, investigators found three rudimentary explosive devices packed with black powder and rigged to a remote-controlled toy car. The remote for the toy car was found inside the SUV, a law enforcement official said. But the bombs didn't detonate and authorities rendered them safe.
Law enforcement personnel moved in on the home in Redlands. They used a robot to sweep for explosives.
In the home and garage, police found 12 pipe bomb-type devices, plus hundreds of tools, many of which could be used to construct improvised explosive devices, or pipe bombs, Burguan said.
Police also found another 2,000 9mm rounds, 2,500 .223 rifle rounds and several hundred more rifle rounds.
At least 14 people were killed. At least 21 others were injured; many by bullets, others in the panic to escape.
The San Bernardino County Coroner released the names of the people killed:
• Robert Adams, 40
• Isaac Amanios, 60
• Bennetta Bet-Badal, 46
• Harry Bowman, 46
• Sierra Clayborn, 27
• Juan Espinoza, 50
• Aurora Godoy, 26
• Shannon Johnson, 45
• Larry Kaufman, 42
• Damian Meins, 58
• Tin Nguyen, 31
• Nicholas Thalasinos, 52
• Michael Wetzel, 37
• Yvette Velasco, 27
A San Bernardino police officer was shot in the leg during the gun battle but was expected to be released from the hospital on Thursday, police said. A sheriff's deputy suffered cuts on the leg, perhaps from shrapnel.
Arrowhead Regional Medical Center and Loma Linda University Medical Center said Thursday, on their respective Twitter sites, that each had five patients.
Unclear. The killers didn't leave a note or any kind of explanation that's been discovered yet.
A workplace grievance may have triggered the shooting, but the number of weapons shows the killers had larger plans, authorities said. Authorities are sure to explore the tenuous links to terror suspects
"If you look at the amount of obvious preplanning that went in, the amount of armaments (they) had, the weapons and the ammunition, there was obviously a mission here," said Bowdich of the FBI. "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. We just don't know."