"We still don't have the motive. There appears to be a degree of planning that went into this," San Bernardino Police Chief Jarrod Burguan said during a press conference Thursday morning.
Fourteen people were killed and 21 others were wounded when suspected shooters Syed Rizwan Farook, 28, and Tashfeen Malik, 29, opened fire during a conference and holiday luncheon Wednesday for the San Bernardino County Health Department at the Inland Regional Center in the 1300 block of S. Waterman Avenue.
San Bernardino officials say the 2 suspects killed are the 2 shooters. They fired 65-75 rounds and had 1 pipe bomb. They wore tactical gear.— ABC7 News (@abc7newsBayArea) December 3, 2015
San Bernardino officials say 12 pipe bombs, 100s of tools to create IEDs or more pipe bombs and 2,000 9mm rounds found at suspects' house.— ABC7 News (@abc7newsBayArea) December 3, 2015
Wearing military-style gear and wielding assault rifles, Syed Rizwan Farook, a 28-year-old county restaurant inspector, and his wife, Tashfeen Malik, 27, slaughtered 14 and wounded 17 in the attack at a social service center shortly after he slipped away from an employee banquet he was attending there.
VIDEO: Gun stores expect to see increase in sales after San Bernardino shooting
It was the nation's deadliest mass shooting since the attack at Sandy Hook Elementary School in Newtown, Connecticut, three years ago that left 26 children and adults dead.
Farook's brother-in-law, Farhan Khan, said the pair got married two years ago. Farook was an American citizen, while Malik was in the United States on a Pakistani passport and had a K1 "Fiance" Visa, according to David Bowdich, assistant director of the Los Angeles FBI office.
Pursuant to U.S. regulations, Farook would have petitioned for Malik to enter the country and they were to be married within 90 days of her entry.
Farook traveled internationally and re-entered the U.S. with Malik in July 2014. Bowdich said the bureau is still investigating which countries Farook visited during his time spent abroad.
FBI says they "still do not know the motive" in the #SanBernadinoShooting. They know it was planned, but don't know why.— ABC7 News (@abc7newsBayArea) December 3, 2015
Hussam Ayloush, executive director of the Council on American-Islamic Relations, told ABC News the suspects dropped their baby off with one of their mothers prior to the attack, claiming they had a doctor's appointment.
Authorities are working to determine the couple's motive, which could include workplace violence or terrorism.
PHOTOS: Scene of mass shooting at San Bernardino social services facility
Farook worked as an environmental inspector for the county for five years, police said, adding that he was at the event earlier Wednesday but left at some point.
"He did leave the party early under some circumstances that was described as angry or something of that nature," Burguan said.
He returned about half an hour later with Malik and opened fire. They were wearing "assault-style clothing" with ammunition attached and carrying assault rifles and semi-automatic weapons.
Farook and his wife sprayed the room with bullets but police didn't know if any one person was targeted.
Police initially reported that there was a third suspect, but now say Farook and Malik were the only two shooters involved in the attack.
A third man who was detained at the scene on Wednesday was determined to have not been involved in the shooting. He was, however, booked on an outstanding misdemeanor warrant.
About four hours after the morning carnage, Farook and Malik were killed in a shootout with police near San Bernardino Avenue and Mountain View, a few miles away from where the attack occurred. Officers fired 380 rounds during the fierce gun battle with the married couple, and the suspects shot 76 rifle rounds at officers.
Police were able to track Farook and Malik down after following "some tips" leading to a home in the nearby city of Redlands. The SUV that they fled in was rented a few days ago, authorities said.
In addition to the two assault rifles and two semi-automatic handguns that were used in the shooting, investigators also found three pipe bomb-style devices that they believed to be explosive devices.
Law enforcement sources tell ABC News all four guns used in the shooting were purchased legally; two were purchased by the shooters and two were purchased by another party.
FBI says female shooter had Pakistani passport, in US on K-1 visa. K-1 nonimmigrant visa allows fiancée in US for 90 days to get married.— ABC7 News (@abc7newsBayArea) December 3, 2015
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Police found over 1,400 rounds for the assault rifles and over 200 rounds for the two handguns inside the black SUV. At the couple's Redlands home, police found 3,000 rounds of ammunition, 12 pipe bomb devices and hundreds of tools that could be used to make improvised explosive devices.
The San Bernardino District Attorney said victim services are available for families affected by the shooting. Those seeking help or services are urged to call (909) 382-3846.
READ MORE: A history of mass shootings in the U.S.
The Associated Press contributed to this story.
Click here for full coverage on the deadly mass shooting in San Bernardino.
Police presser: "We do not have a motive" for San Bernardino shootings— Brian Ross (@BrianRoss) December 3, 2015
The neighborhood b/w Richardson & Mt. View South of SB Ave is no longer sheltering in place. A person of interest has been detained.— SB County Sheriff (@sbcountysheriff) December 3, 2015
FBI, ATF, SBPD and #SBCSD are all in unified command in this incident. A third suspect may be outstanding.— SB County Sheriff (@sbcountysheriff) December 3, 2015
Two suspects confirmed dead. 1 male & 1 female. The vehicle was cleared of any explosive devices.— SB County Sheriff (@sbcountysheriff) December 3, 2015
ATF Explosives Enforcement Officer investigating a suspected pipe bomb recovered from a suspect, law enforcement official says.— ABC News (@ABC) December 2, 2015
There is an active scene unfolding in San Bernardino. Preliminary info is a suspect is down, officers are ok. Not confirmed if related.— SB County Sheriff (@sbcountysheriff) December 2, 2015
ACTIVE SHOOTER:Area of Orange Show Rd/ Waterman Ave near Park Center, & surrounding area remains VERY ACTIVE. AVOID! pic.twitter.com/5vG0aYW6IL— SB County Sheriff (@sbcountysheriff) December 2, 2015