A mass shooting at the Inland Regional Center in San Bernardino that left 14 dead and 21 others injured was being investigated as an act of terrorism, the FBI announced Friday.
“As of today, based on the information and the facts as we know them, we are now investigating these horrific acts as an act of terrorism,” Dave Bowdich of the FBI said at a Friday morning news conference.
The declaration came two days after Syed Farook, 28, and Tashfeen Malik, 27, stormed into a County of San Bernardino Department of Public Health training and holiday luncheon at the center, spraying a room full of Farook's coworkers with bullets.
Federal investigators have uncovered evidence that pointed to extensive planning ahead of the deadly attack, Bowdich said.
Although he didn't specify the evidence, he said there were a number of pieces "that has essentially pushed us over the cliff to say we are now investigating this as an act of terrorism.”
He did not link the attack to any terror group, including Islamic State, saying they were still working with the agency's foreign partners to determine any overseas connections.
Earlier in the day, three U.S. officials told CNN that Malik had declared her loyalty to the leader of ISIS on Facebook, apparently posting it on the social media site as the massacre occurred.
Bowdich said the FBI was aware of the post, and was looking into it. He offered no additional information on the post.
Authorities were also looking into Farook's communications via social media and phone with at least one subject who was being investigated for possible terror connections, according to CNN.
Bowdich confirmed that at least one of the two individuals involved had "telephonic connections" with other subjects being investigated by federal officials.
He did not specify if it was Farook or Malik, declining to elaborate further on the matter.
Fourteen victims, all between the ages of 26 and 60, were killed and 21 others were injured in Wednesday's attack, the deadliest since 20 children and six staff members were killed in the Sandy Hook Elementary School shooting in 2012.
San Bernardino Police Chief Jarrod Burguan confirmed most of the victims worked for the county.
He said Farook, an American, was employed by the county's health department and had attended the luncheon that morning.
Farook left the party angry, possibly after a dispute. Others told authorities he seemed to have just disappeared from the venue.
He later returned to the party with Malik, his wife, wearing “black-style tactical gear,” and began shooting at party attendees, according to police.
The couple was heavily armed and “came prepared,” Burguan said Wednesday. They fired 65 to 75 rounds at the luncheon before fleeing in a rented black SUV.
Three pipe bombs attached to a remote-controlled car were also later discovered by first responders, according to the chief.
Several hours after the deadly rampage, the couple was killed during a shootout with law enforcement officers. According to Burguan, the suspects fired 76 rounds at the officers, who fired about 380 in return during the gunbattle.
The four guns used by Farook and Malik were all purchased legally, Burguan said. Two of the handguns were bought by Farook, while an unidentified person obtained the other two firearms.
The couple had been married for about two years, after Farook returned from a 2013 overseas trip to several countries, including Pakistan, where Malik was from, Bowdich said.
CNN reported that he went to Saudi Arabia, but the FBI official was unaware of the other countries Farook visited during the trip.
It was not known what role, if any, Farook's travels played in the attack, the FBI official said at the news conference.
Neither appeared on any federal list of potentially radicalized people, according to CNN.
Bowdich would not comment on whether anyone else was being investigated as a suspect in connection to the case. No other arrests, however, have been made.
"It's possible there may be some in the future," he said.
Bowdich stressed the FBI was still in the early stages of the investigation, and that the process of searching for evidence was ongoing.
All resources were being utilized to find "every piece" of available evidence out there, including digital media, phone calls, emails and intelligence, he stated, adding that the information would hopefully point them to a motive for the terror attack.
Bowdich added that the couple had “attempted to destroy their digital fingerprints,” even crushing their cellphones and throwing them away in a nearby trash can. They were recovered by federal authorities, who were working to obtain the data from the devices.
The FBI has already completed its investigation at the Redlands residence Farook and Malik had apparently rented, according to Bowdich.
"That takes time, it's not a three-day process," he told reporters.
Anyone with information about the case is encouraged to contact the FBI by calling 1-800-225-5324.
KTLA's Ashley Soley-Cerro and the CNN Wire contributed to this story.