As many as three gun-wielding assailants opened fire on a holiday party for county employees Wednesday, killing 14 people in the deadliest mass shooting in the United States since the Sandy Hook Elementary School massacre three years ago this month.

Hours after the shooting, law enforcement officials said two attackers — a man and a woman, neither identified by name — had been killed in a police shootout several miles from the site of the original attack. A third suspect who had been seen fleeing the scene was taken into custody, but police said they were not sure whether he had been one of the shooters.

An FBI official said at an evening news conference that authorities could not rule out the possibility that terrorism was the motive.

“One of the big questions that will come up repeatedly is, ‘Is this terrorism?’ ” said David Bowdich, assistant director in charge of the FBI’s Los Angeles office. “It is a possibility. We are making some adjustments to our investigation. It is a possibility. But we don’t know that yet. And we are not willing to go down that road yet.”

A senior U.S. law enforcement official identified one of the suspects as Syed Farook. Records show a Syed Farook works as a health inspector for the San Bernardino County Department of Public Health, which was hosting Wednesday’s holiday party.

The attack spawned a tense, confusing and terrifying day in Southern California as the shooters — their number unclear, their identities unknown, their motives unimaginable — fled the scene in a black SUV and eluded capture for hours.

Police followed a tip that led them to a house in the nearby city of Redlands, where records show a Syed Farook once lived. During a stakeout there, they spotted an SUV that matched the description of the suspects’ vehicle, and when the occupants drove away, police gave chase. A law enforcement source said the suspects threw objects — possibly pipe bombs — out the window.

The suspects drove back into San Bernardino and, reaching a residential neighborhood, stopped and began exchanging gunfire with police. One officer was injured in the firefight, but police said the wounds were not life-threatening.

The two suspects were killed, their vehicle riddled with bullets.

The immediate aftermath was captured by helicopter new crews, who provided a live feed to a national audience watching on television and online. Police officers swarmed the neighborhood, guns drawn, taking cover behind walls and armored SWAT vehicles. Three armored vehicles surrounded the SUV, and officers slowly and methodically determined that no one inside had survived the hail of gunfire.

The two slain suspects were armed with assault rifles and handguns, San Bernardino Police Chief Jarrod Burguan said at an evening news conference.

At least 17 people were being treated in local hospitals for injuries suffered in the late-morning rampage. A spokeswoman for Loma Linda University Medical Center said two of the five patients treated there were in critical condition.

The Inland Regional Center is a three-building complex that houses a conference center and serves more than 30,000 people with developmental disabilities. The attack occurred in the conference center’s first-floor banquet room, where the San Bernardino County public health department was hosting a holiday party, complete with Christmas trees and other decorations.

Witnesses reported seeing three people in black clothing using long guns akin to assault weapons. Recent mass shootings in the United States have typically involved a lone gunman, often someone mentally unstable or consumed with rage. Multiple-shooter events are extremely rare: According to a recent FBI report on 160 active shooting incidents between 2000 and 2013, all but two involved a single shooter.

“They came prepared to do what they did as if they were on a mission,” Burguan said. “They were dressed and equipped in a way that indicate they were prepared.” (Washington Post)