The terrorists made the declaration on their official radio station Saturday, days after the Wednesday attack that also left 21 injured.
Tashfeen Malik and her husband, Syed Rizwan Farook, burst into a holiday party for the environmental health department in San Bernardino.
After spraying Farook’s co-workers with bullets, they took police on a manhunt that paralyzed the city. The couple died in a shootout with authorities the same day.
“We pray to God to accept them as martyrs,” al-Bayan Radio reported.
‘Act of terrorism’
A day before the terror group said the shooters were its supporters, the FBI had said it is treating the attack as an “act of terrorism.” The FBI took over the investigation from local authorities Friday.
There was “evidence … of extreme planning” of the killings, said David Bowdich, assistant director of the FBI office in Los Angeles.
ISIS used the word “supporters,” which differs from its previous references to “knights” or “soldiers.” The declaration does not necessarily mean the terror group issued a directive to the attackers. ISIS has consistently urged supporters to carry out lone wolf attacks, and the couple may have been answering a vague, general call.
While the attack was underway, the female shooter posted a pledge of allegiance to ISIS leader Abu Bakr al-Baghdadi on Facebook, three U.S. officials told CNN.
The post was made on an account with a different name, one U.S. official said. Facebook said it later took it down because it violated community standards that prohibit the promotion of terrorism or the glorification of violence.
Facebook declined to go into details about the nature of the post.
Inspired by ISIS?
The mass shooting may have been inspired by ISIS, a law enforcement official said, but none of the officials said ISIS directed or ordered the attack.
“This is looking more and more like self-radicalization,” a law enforcement official said.
Relatives had no idea that the couple held radical views, according to family lawyers.
Nor did they know the couple had a makeshift bomb lab in the apartment they shared with their 6-month-old daughter.
‘It doesn’t add up’
“It just doesn’t make sense for these two to be able to act like some kind of Bonnie and Clyde or something,” Farook’s family attorney David S. Chesley said.
“It’s just ridiculous. It doesn’t add up.”
A law enforcement source said another option investigators are looking into is whether a workplace issue with religion may have sparked the killings.
The couple did not have any trouble with the law nor were they on any list of potentially radicalized people.
Malik was born and raised in Pakistan and moved to Saudi Arabia at age 19. It’s not known what connections she may have had with any terrorists or groups.
Investigators are exploring Farook’s communications with at least one person who was under investigation for possible terror connections. Some were by phone, some on social media.
Family lawyer Mohammad Abuershaid said that Farook traveled twice to Saudi Arabia — first in 2013 for the Hajj, the annual pilgrimage to Mecca that Muslims are required to make at least once in their lifetimes, then again to marry Malik, whom he’d met through an online dating service.
The FBI said he went to Pakistan as well, but the family attorneys denied that.
Shortly after the massacre, authorities searched the couple’s house and found pipe bombs, thousands of rounds of ammunition and more guns.
The shooters didn’t make it easy for authorities to track their digital footprints.
The hard drive from their computer is gone, and two relatively new cell phones were found smashed in a garbage can near the shooting scene, law enforcement officials said.
As the city remains on edge, a bomb squad inspected a package at a UPS facility in Southern California late Friday after a driver discovered it was addressed to the home of the shooters.
The UPS driver noticed a package headed for delivery had their Redlands townhouse address, San Bernardino Police Chief Jarrod Burguan tweeted.
It was returned to the distribution facility, where bomb technicians said it was safe and “posed no threat.”
Burguan did not say what was in the package.