The Muslim couple who stormed an office holiday party Wednesday in Southern California, mowing down 14 people before dying hours later in a shootout with police, possessed a massive arsenal of ammo, bombs and high-powered weapons -- and investigators were hoping that computer drives and cell phones seized from their home could tell them whether they were radicalized terrorists with more targets in their sights.

Local and federal authorities - as well as President Obama - continued Thursday to resist calling the carnage at a San Bernardino social services facility terrorism, even as evidence mounted that the pair, who wore tactical gear and moved with grim precision, may have been jihadists armed to the teeth and hellbent on slaughtering innocent Americans. More than 5,000 rounds of ammunition were later found in their home, which sources described as "an IED factory" packed with explosives and bomb-making equipment. 

"At this stage, we do not yet know why this terrible event occurred," Obama said in an address from the White House. "We'll get to the bottom of this and be vigilant getting the facts before we issue decisive judgments on how this occurred."

Syed Rizwan Farook, a U.S.-born citizen of Pakistani descent who had traveled to Saudi Arabia for nine days in the summer of 2014 and had recently begun wearing a full beard, and Tashfeen Malik, 29, burst into the facility Wednesday morning and sprayed up to 75 rounds at Farook's own terrified colleagues in a conference room where his employer, the county health department, was hosting a holiday party Farook had angrily bolted only minutes earlier. The pair escaped in a black SUV after the attack, which authorities said was over within as few as 10 minutes, only to resurface three hours later and less than 2 miles away in a fierce gun battle on the city's main drag.

"They came prepared to do what they did, as if they were on a mission," said San Bernardino Police Chief Jarrod Burguan, who refuted an earlier report by Fox News that the suspects wore GoPro cameras during their initial rampage.

"They came prepared to do what they did as if on a mission."

- San Bernardino Police Chief Jarrod Burguan

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Farook, 28, who authorities said was born in Illinois, and raised in California and had worked as a $51,000-per-year restaurant inspector at the San Bernardino County Department of Public Health for five years, was described by co-workers as a "devout" Muslim, who lived with his wife, child and grandmother in a home in nearby Redlands, which sources described as "an IED factory." Bomb squads working with robots swept the home late into the night Wednesday, and witnesses reported hearing several explosions. Malik, who had a 6-month-old baby with Farook, came to the U.S. on a K-1 (fiance of citizen) visa and had a Pakistani passport, according to authorities. It was not clear how long the couple had been together.

Burguan said Thursday he was "not aware of any notes" that might shed light on a possible motive. A source briefed on the investigation told Fox News Farook had been in contact with individuals who had been the subject of previous terrorism FBI investigations, but those investigations had been closed.

Meanwhile, jihadists and extremists took to social media to express joy over the American casualties, according to the Middle East Media Research Institute (MEMRI).

One user, Muhammad Abu Ubaida, tweeted: "Allah Akbar, and thanks for Allah, the killing of at least 30 people in a shooting incident in San Bernardino in California," under the hashtag, “America Burning.”

Muslimah, a prominent pro-ISIS account, shared a photo believed to be of Syed Farook, and wrote: "May Allah accept our brother & sister who were martyred after carrying out an operation against Crusaders in USA," MEMRI said.

At an afternon news conference, Attorney General Loretta Lynch said the FBI had taken the reins of the investigation, and a bureau spokesman said a focus of the probe is digital evidence collected from their homes, including hard drives, thumb drives and cell phones. While those could be part of a terror investigation, and FBI spokesman said it was too soon to ascribe religion as a motive.

"It is a possibility, but we don't know that," said Assistant Regional FBI Director David Bowdich. "It's possible it goes down that road. It's possible it does not."

A law enforcement source told Fox News that the couple were each carrying an AR-15 rifle and a pistol when they were shot and killed by police after a brief chase in their rented black Ford Expedition with Utah plates about 2 miles from the initial shooting site. The source said the vehicle also contained so-called "rollout bags" with multiple pipe bombs, as well as additional ammunition.

"That's a military tactic for a sustained fight," the source told Fox News of the rollout bags.

The guns found on the suspects, two rifles and two handguns, were purchased legally, according to Meredith Davis, a spokeswoman for the Bureau of Alcohol, Tobacco, Firearms and Explosives. Burguan said Thursday Farook had purchased the handguns, but he did not say who had bought the rifles.

It was unclear where the suspects may have been during the hours following the lightning-quick attack, but they did not get far. A police spokeswoman said police came across the SUV while "doing follow-up work," and several reports said the car was at a nearby home police were staking out when the suspects got in and tried to flee. It was not immediately clear if that home was the one searched later in Redlands.

About three hours after the shooting, with police looking for a dark SUV, officers staking out the Redlands home after being tipped off by a colleague disturbed by Farook's exit from the party saw a vehicle matching that description. Word that police were hot on their trail came even as emergency responders were treating the wounded on the scene, and sparked a flurry of law enforcement racing to the scene just blocks away. The gunfight, caught on cellphone video by a bystander, was a furious exchange in which 23 officers fired a total of 380 rounds at the suspects, according to Burguan. Two officers suffered non-life threatening injuries.

In addition to the explosives found in the SUV, authorities discovered and detonated three pipe bombs late Wednesday at the Inland Regional Center, the complex where the initial shooting took place about 60 miles east of Los Angeles. Another source said investigators discovered a dozen pipe bombs in the house, as well as small explosives strapped to remote-controlled cars - a signature of terrorist groups including Al Qaeda, according to counter-terrorism experts. Police also found thousands of .223-caliber and 9mm rounds at the home.

""Clearly they were equipped and could have done an other attack," Barguan said. "Luckily we stopped them before that."

The initial shooting happened shortly before 11 a.m. local time at the state-run center, which includes three buildings where developmentally disabled people of all ages are treated. The conference area had been rented out by Farook's colleagues for a holiday banquet, according to authorities. Burguan said that Farook had angrily left the party before returning with Malik, however, other investigators doubted the shooting could be chalked up to a workplace dispute, due to the apparent planning behind the attack as well as the heavy weaponry used. On Thursday, officials raised to 21 the number of people injured in the attack.

Patrick Baccari, a co-worker of Farook who suffered minor wounds from shrapnel slicing through the building's bathroom walls, told The Associated Press he had been sitting at the same table as Farook at the banquet before his colleague suddenly disappeared, leaving his coat on his chair.

Baccari also said that Farook had traveled to Saudi Arabia for about a month this past spring. When Farook came back, word spread that he had gotten married and the woman he described as a pharmacist joined him shortly afterward. Baccari added that the reserved Farook showed no signs of unusual behavior, although he grew out his beard several months ago. A five-year-old profile for Farook on a dating site said he was "religious" and enjoyed hanging out in the "back yard doing target practice with younger sister and friends."

Center employees, who undergo monthly training drills to prepare for active shooter situations, initially thought the incident was a drill, according to the Los Angeles Times. But when real bullets flew, several hid in closets, barricaded themselves in rooms or fled for their lives.

The Inland Regional Center is one of 21 facilities serving people with developmental disabilities run by the state, said Nancy Lungren, spokeswoman for the California Department of Developmental Services. The social services agency administers, authorizes and pays for assistance to people with disabilities such as autism and mental retardation. On an average day, doctors at the regional centers would be evaluating toddlers whose parents have concerns and case workers meeting with developmentally disabled adults.

Fox News' Adam Housley and Catherine Herridge contributed to this report.