San Bernardino — California gunman Syed Rizwan Farook had been in contact with known Islamic extremists on social media, a US intelligence official said on Thursday.
The details emerged as investigators tried to determine whether the rampage that left 14 people dead was terrorism, a workplace grudge or some combination.
The husband-and-wife killers were not under FBI scrutiny before the massacre, said a second US official, who likewise was not authorised to discuss the investigation and spoke on condition of anonymity.
Wearing black tactical gear and wielding assault rifles, Farook, a 28-year-old county restaurant inspector, and his wife, Tashfeen Malik, 27, sprayed as many as 75 rounds into a room at a social service center for the disabled, where about 75 of Farook's co-workers had gathered on Wednesday morning. Farook had attended the event but slipped out and returned in battle dress.
Four hours later and two miles away, the couple died in a furious gunbattle in which they fired 76 rounds, while 23 law officers unleashed about 380, police said.
On Thursday, Police Chief Jarrod Burguan offered a grim inventory that suggested on Wednesday's bloodbath could have been far worse.
At the social service center, the couple left three rigged-together pipe bombs with a remote-control detonating device that apparently malfunctioned, and they had more than 1 600 rounds of ammunition remaining when police killed them in their rented SUV, Burguan said.
At a family home in the nearby town of Redlands, they had 12 pipe bombs, tools for making more, and over 3 000 additional rounds of ammunition, the chief said.
‘We don’t know the motivation’
"We don't know if this was workplace rage or something larger or a combination of both," Attorney General Loretta Lynch said in Washington, echoing President Barack Obama. "We don't know the motivation."
Investigators are trying to determine whether Farook, who was Muslim, became radicalised — and, if so, how — as well as whether he was in contact with any foreign terrorist organization, said the US intelligence official, who was not authorised to discuss the matter publicly and spoke on condition of anonymity.
The same official said Farook had been in touch on social media with extremists who were under FBI scrutiny.
The second US official said the FBI was treating the attack as a potential act of terror but had reached no conclusion that it was. The official said Farook's contacts online did not involve any significant players the FBI knew of and dated back some time, with there was no immediate indication of a recent surge in communication.
Some posts deleted
The official cautioned that such contact by itself doesn't mean someone is a terrorist.
Rita Katz, director of SITE Intelligence Group, an organisation that tracks and analyses extremists, said it hasn't found any connection between Farook and jihadi groups. But she also said that some of Farook's social media posts seem to have been deleted before the attack.
Wednesday's rampage was the nation's deadliest mass shooting since 2012, when 26 children and adults were slain in Newtown, Connecticut.
In San Bernardino, a Southern California city of 214 000, the victims ranged in age from 26 to 60. A further 21 people were injured, including two police officers, authorities said. Two of the wounded remained in critical condition on Thursday.
Nearly all the dead and wounded were county employees.
Authorities said the attack was carefully planned.
"There was obviously a mission here. We know that. We do not know why. We don't know if this was the intended target or if there was something that triggered him to do this immediately," David Bowdich, assistant director of the FBI's Los Angeles office, said as the bureau took over the investigation.
No criminal record
Farook has no known criminal record, Burguan said. He was born in Chicago to a Pakistani family, raised in Southern California and worked at San Bernardino County's Department of Public Health for two stints totaling four years since 2010, according to authorities and acquaintances. The Saudi Embassy said he travelled to Saudi Arabia in the summer of 2014 for nine days.
As for Malik, she came to the US in July 2014 on a Pakistani passport and a fiancée visa, authorities said. To get the visa, immigrants submit to an interview and biometric and background checks — screening intended to identify anyone who might pose a threat.
They were married on August 16, 2014, in nearby Riverside County, according to their marriage license. Both listed their religion as Muslim.
The couple had a 6-month-old daughter who they dropped with relatives on Wednesday morning before the shooting.