Police believe that 28-year-old Syed Rizwan Farook, an inspector with the department, left the party following a dispute and returned with his partner, 27-year-old Tashfeen Malik, to carry out the shooting.
The suspects were armed with two "long guns" - rifles or shotguns - and two semi-automatic handguns and wore dark, military-style clothing, police said. They killed 14 people and wounded 17 more.
Police engaged in a shoot-out with the suspects as they attempted to flee the scene in a dark SUV, and killed both. A third person seen running from the area was detained, but police said it was unclear whether the person was involved.
Several possible explosive devices were found at the scene, police said. San Bernardino police chief Jarrod Burguan said there "had to be some degree of planning" behind the attack.
The attackers
Police engaged in a firefight with two suspects in a black SUV, killing both
Farook and Malik were in a relationship and possibly married. Police officials said Farook had worked for the county public health department for five years.
Two colleagues who survived the attack told the LA Times they were shocked to hear Farook's name linked to the shooting. He was quiet and polite with no obvious grudges, they said.
Farook recently travelled to Saudi Arabia, according to the Times, and returned with a new wife he had met online. The couple had a baby and appeared to be "living the American dream," Patrick Baccari, a fellow health inspector, told the paper.
The couple dropped their six-month-old daughter with Farook's mother in Redlands, according to the LA Times report. The grandmother reportedly grew worried when she heard about the shooting and attempted to reach her son by phone but failed.
The third person who was detained has not been identified, but Mr Burguan said police believe there were only two shooters.
http://www.bbc.com/news/world-us-canada-34993344