Police have killed a married couple suspected of shooting dead 14 people and wounding 21 more in San Bernardino, California. Here's what we know.
The attack took place at a Christmas party on Wednesday for employees of the San Bernardino public health department, at the Inland Regional Centre, which provides services for people with developmental disabilities.
Police believe that 28-year-old Syed Rizwan Farook, an inspector with the department, left the party and returned with his wife, 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.
Police engaged in a shoot-out with the suspects as they attempted to flee the scene in a dark SUV, and killed both.
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.
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.
According to the AP News Agency, one victim of the shooting, Nicholas Thalasinos, got into a heated discussion with Farook about whether Islam was a peaceful religion while working a few weeks ago.
His friend Kuuleme Stephens said she did not know whether those debates were a factor in the attack.
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 FBI is interviewing Enrique Marquez, a close friend of Farook's who bought the assault rifles used in the shooting.
Mr Marquez and Farook were reportedly plotting an attack in 2012, but decided against it after law enforcement activity and arrests in the area.
Farook and Malik had practiced shooting at a local gun range just days before the attack, the FBI said, and that the two had been radicalised "for some time".
Authorities have now named the 14 victims of the attack, who are mostly county employees. They are
- Yvette Velasco, 27
- Larry Kaufman, 42
- Damian Meins, 58
- Sierra Clayborn, 27
- Nicholas Thalasinos, 52
- Mike Raymond Wetzel, 37
- Robert Adams, 40
- Bennetta BetBadal, 46
- Isaac Amanios, 60
- Aurora Godoy, 26
- Harry Bowman, 46
- Tin Nguyen, 31
- Juan Espinoza, 58
- Shannon Johnson, 45
The FBI is investigating the attack as an act of terrorism.
Authorities found two mobile phones that had been crushed in a trash bin nearby the attackers' home and are closely examining the data they can extract from them.
"I'm ready to confirm there are some telephonic connections and other subjects of our investigation," said FBI assistant director David Bowdich.
"There's a number of pieces of evidence that has essentially pushed us off the cliff to say that this is an act of terrorism."
US officials have told the media Tashfeen Malik pledged allegiance to the leader of the Islamic State (IS) group on Facebook.
The US government did not pick up on extremist messages posted online when Farook and his wife began chatting.
Farook and Malik talked about martyrdom and jihad as early as 2013, but they did not get on authorities' radars. Malik gained entry to the US on a fiancée visa, despite her radical views expressed online.
The Inland Regional Center, where the shooting took place, provides services for people with developmental disabilities, but the shooting appeared to be unrelated to its clients.
The incident qualifies as a mass shooting and is at least the second in a week, following a shooting at a planned parenthood clinic in Colorado on Friday.
According to the Gun Violence Archive, a US non-profit organisation which tracks gun violence, there have been 310 verified mass shootings in the country so far this year.
"We have a pattern now of mass shootings in this country that has no parallel anywhere else in the world," said President Obama following the incident.
California gun law
Police said they recovered two "long guns" - assault rifles or shotguns - and two semi-automatic handguns from the scene. Two of the four weapons used in the shooting were purchased legally, said Meredith Davis, a spokesman for the Bureau of Alcohol, Tobacco and Firearms (ATF).
California has relatively strict gun laws, compared with other US states. Anyone wishing to purchase a gun must have a Firearm Safety Certificate, and guns have to comply with state-specific regulations.
There is a mandatory 10-day waiting period for most purchases, and weapons must be bought through a licensed dealer.