SAN BERNARDINO, Calif. (AP) — At least two heavily armed attackers opened fire on a banquet at a social services center for the disabled Wednesday, killing 14 people and seriously wounding more than a dozen others in a precision assault that looked “as if they were on a mission,” authorities said.

Hours later, police hunting for the killers riddled a black SUV with gunfire in a shootout two miles from the late-morning carnage, and a man and woman with assault rifles, handguns and “assault-style clothing” were killed, San Bernardino Police Chief Jarrod Burguan said.

A third person who was spotted running near the gunbattle was detained, but Burguan said it was unclear if that person had anything to do with the crime.

It was the nation’s deadliest mass shooting since the attack at a school in Newtown, Connecticut, three years ago that left 26 children and adults dead.

Police shed no light on the motive for the massacre, but David Bowdich, assistant director of the FBI’s Los Angeles office, said the bureau is looking at several possibilities, including workplace violence and terrorism. He did not elaborate.

The attackers invaded the Inland Regional Center and began shooting around 11 a.m. They opened fire in a conference area that the San Bernardino County Department of Public Health had rented out for a banquet, said Marybeth Feild, president and CEO of the nonprofit center.

Police spokeswoman Sgt. Vicki Cervantes said witnesses reported seeing one to three gunmen.

“They came prepared to do what they did, as if they were on a mission,” the police chief said.

Burguan said that someone had left the county employees’ event after “there was some type of dispute,” but investigators were not sure whether that had anything to do with the subsequent massacre in the Southern California city of 214,000 people about 60 miles of Los Angeles.

Authorities also found a potential explosive device at the social service center.

As gunfire echoed through the large three-building complex, several people locked themselves in their offices, desperately waiting to be rescued by police. Some texted their loved ones or telephoned them and whispered to them what was going on.

“People shot. In the office waiting for cops. Pray for us. I am locked in an office,” Terry Petit’s daughter texted him.

Petit, choking back tears as the read the text for reporters at the shooting scene, said his daughter works at the center, where social workers find jobs, housing and transportation and provide other services to people with disabilities such as autism, cerebral palsy and epilepsy.

Ten of the wounded were hospitalized in critical condition, and three were in serious condition, Fire Chief Tom Hannemann said.

That the violence happened at a place dedicated to helping people with developmental disabilities made it even harder for some to comprehend.

“These are all disabled kids, very disabled,” said Sherry Esquerra, who was searching for her daughter and son-in-law, both of whom work at the center. “She gets all the services she possibly could for these kids. So I just don’t understand why somebody would come in and start shooting.”

FBI agents and other law enforcement authorities converged on the center and searched room to room for the attackers, but they had apparently escaped.

One witness, Glenn Willwerth, who runs a business across the street, said he heard 10 to 15 shots and then saw an SUV with blacked-out windows pull out “very calmly, very slowly” and drive off.

Triage units were set up outside the center, and people were wheeled away on stretchers. Others walked quickly from a building with their hands up so that police could search them and make sure the attackers weren’t trying to slip out.

As the manhunt dragged on, stores, office buildings and at least one school were locked down in the city, and roads were blocked off.

About four hours later, with police looking for a dark SUV, officers staking out a home in the nearby city of Redlands saw a vehicle matching that description leave. They tried to pull it over, the SUV crashed, and a gunbattle broke out around 3 p.m., authorities said. One officer suffered a minor injury.

President Barack Obama was briefed on the attack by his homeland security adviser. He said it was too early to know the shooters’ motives but urged the country to take steps to reduce mass shootings, including stricter gun laws and stronger background checks.

“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, and there’s 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,” Obama told CBS.

The shooting sounded like “an organized plot,” and preliminary information seems to indicate that “this is personal, and there seems to suggest some element of revenge and retaliation,” said Erroll G. Southers, director of Homegrown Violent Extremism Studies at the University of Southern California and a former FBI agent.

“What it says to me, it’s someone who’s familiar with the facility, it’s someone who knew exactly what room they were going to go to. They knew exactly which way they needed to escape,” Southers said. “They’ve done their homework. They know what the response time in this jurisdiction.”

Marcos Aguilera’s wife was in the building when the gunfire erupted. He said a shooter entered the building next to his wife’s office and opened fire.

“They locked themselves in her office. They seen bodies on the floor,” Aguilera told KABC-TV, adding that his wife was able to get out of the building unharmed.

The social services center has two large buildings that require a badge to get in, said Sheela Stark, an Inland Regional Center board member. However, the conference room where many public events take place — including the banquet on Wednesday — is usually left open when visitors are expected.