US authorities are investigating the motive behind a shooting spree that left 14 people dead and another 17 wounded at a social services centre hosting a Christmas party in Southern California.
A man and a woman suspected of taking part in Wednesday's attack in San Bernardino died in a shoot-out with police hours later, authorities said on Thursday.
The slain suspects were identified by police as Syed Farook, 28, and Tashfeen Malik, 27, were described as a couple.
Jarrod Burguan, San Bernardino police chief, said US-born Farook had attended a holiday banquet for employees of the local public health department, and later returned to open fire on the celebration.
The attackers were dressed in military-style gear and carried assault weapons as they burst into the auditorium where the shooting took place, at the campus of a social-services agency.
The couple also placed several bombs at various locations, which police detonated. In addition to the 14 dead, the shooting left at least 21 people wounded, including 10 in critical condition.
Police said the weapons the suspects used were obtained legally, adding that the suspects had no criminal records, and were not under any police surveillance prior to the incident.
At the time that the shootout happened, the suspects were carrying over a thousand rounds of ammunition, according to authorities.
Police were conducting a house-to-house search in the area where the third suspect was apprehended and completed the search early in the evening, when the "shelter-in-place" warning to residents was lifted, according to police.
Police, however, said later that they determined that the third person who was apprehended was not a suspect.
"This is the first time we've seen it like this, on lockdown," Hector Guerrero, husband of an employee who works in the facility, told Al Jazeera.
"I don't think anything like this has happened in the Inland Empire," he said, referring to the area east of Los Angeles.
OPINION: The ethnicity of San Bernardino shooters doesn't matter
Farook's brother-in-law has said he was stunned to hear of his relative's involvement in Wednesday's shooting.
Farhan Khan, who is married to the sister of Syed Farook, made the comments at the Anaheim office of the Council on American-Islamic Relations.
Khan, who said he last spoke to Farook about a week ago, said he had "absolutely no idea why [Farook] would do this. I am shocked myself".
The latest killings are likely to fuel to an ongoing debate about the definition of "terror attacks" in the US and what role the ethnicity of perpetrators play in media coverage of gun violence.
READ MORE: California shooting, misinformation and 'Bin Ardogan'
Al Jazeera's Rob Reynolds, reporting from San Bernardino, said: "The nomenclature is very troubling in the US. What defines terrorism? Is it simply someone with a political motive, is it someone who kills a number of people for motives that are unknown? School shootings, work place shootings - these things happen all the time in the US."
President Barack Obama, who just last week made a plea for tougher gun-control measures after three people were killed at a family-planning centre in Colorado, again urged Congress to take action.
In the Colorado Springs attack, a man killed three people and wounded nine in a shooting rampage at a Planned Parenthood clinic .
In October, an armed man killed nine people at a college in Oregon, and in June, a white attacker killed nine black churchgoers in South Carolina.
| The attackers fled the scene, prompting an intense manhunt and a shootout with police [Mike Blake/Reuters]
"The one thing we do know is that we have a pattern now of mass shootings in this country that has no parallel anywhere else in the world," Obama told CBS News.
"There are some steps we could take, not to eliminate every one of these mass shootings, but to improve the odds that they don't happen as frequently."
Wednesday's attack marked the deadliest gun violence in the country since the massacre at Sandy Hook Elementary School in Newtown, Connecticut, in December 2012, in which 27 people, including the shooter, were killed.
So far in 2015, there have been more than 350 shootings in which four or more people have been wounded, according to the crowd-sourced website shootingtracker.com, which keeps a running tally of US gun violence.
Source: Al Jazeera and agencies