San Bernardino shooters 'supporters' of ISIS, terror group says

It also came after reports that Malik made a public declaration of loyalty to ISIS' leader while the attack was underway. Three U.S. officials familiar with the investigation told CNN on Friday that Malik posted to Facebook a pledge of allegiance to ISIS leader Abu Bakr al-Baghdadi.

The couple's motivation for the attack is a key focus for investigators. But ISIS' acknowledgment of Malik and Farook as supporters doesn't mean they were members or that someone from the group ordered it, said retired Air Force Lt. Col. Rick Francona, a CNN military analyst and a former intelligence officer.

ISIS, when claiming responsibility for other terrorist attacks, would call attackers "knights" or "soldiers" rather than supporters. It has, however, urged sympathizers to carry out attacks on their own.

"What they're calling these two are supporters, which is kind of a lesser level," indicating it might not have had direct contact with the couple, Francona said.

On Saturday morning, officials briefing President Barack Obama about the investigation told him that they had "no indication that the killers were part of an organized group or a broader terrorist cell," the White House said.

Authorities searched the California house of the person who bought two of the rifles used by Farook, a federal law enforcement source said Saturday.

The source was not at liberty to discuss what was being sought or what was taken away -- if anything -- from the house because the warrant application was filed under seal.

Authorities are turning to phone, travel, computer and other records to determine why the couple committed the attack and had what amounted to a makeshift bomb lab in the rented Redlands townhouse they shared with their 6-month-old daughter.

The FBI took over the investigation from local authorities Friday, saying it was treating the attack as an "act of terrorism."

There was "evidence ... of extreme planning" of the killings, said David Bowdich, assistant director of the FBI office in Los Angeles.

The mass shooting may indeed have been inspired by ISIS, a law enforcement official told CNN this week, but no official has told CNN that ISIS directed or ordered the attack.

"This is looking more and more like self-radicalization," a law enforcement official said on condition of anonymity.

A law enforcement source said another option investigators are looking into is whether a workplace issue with religion may have sparked the killings.

One notable piece of evidence will be Malik's alleged online allegiance pledge to al-Baghdadi. Facebook said it took the post 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.

Farook, 28, was born in Illinois and raised in California. He 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, and then then again to marry Malik, whom he'd met through an online dating service, said Farook family attorney Mohammad Abuershaid.

The FBI said he went to Pakistan as well, but the family attorneys denied that.

Malik was born and raised in Pakistan and moved to Saudi Arabia around the age of 18 or 20, Abuershaid said.

She came to the United States on a fiancée visa and became a legal permanent resident.

Malik was 29, according to her Pakistani national identification card -- a photocopy of which was obtained by CNN from a senior Pakistani intelligence source -- and her marriage certificate.

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.

"These appear to be soft connections," an official said, meaning they were not frequent contacts. Farook's last communication with the contacts was months ago.

A federal official said Farook has "overseas communications and associations," but it's not yet clear how relevant they are to the shootings. "We don't know yet what they mean," the official said.

The couple did not have any trouble with the law, nor were they on any list of potentially radicalized people.

Relatives had no idea that the couple held radical views, according to family lawyers.

"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."

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.

Investigators believe the shooters left at the massacre site a remote-controlled toy car, strapped with three rudimentary explosive devices. The remote for the car was found inside the SUV where Farook and Malik were later killed, a law enforcement official said.

The pair apparently planned to use the remote to detonate the explosives from a distance, and either it didn't work or they didn't do it, the official said.

Authorities are looking into whether the device was connected in any way to al Qaeda's Inspire magazine, the FBI's Bowdich said this week.

Al Qaeda's Inspire, plus ISIS' Dabiq magazine, are two examples of media the terror networks have used to call on people to commit attacks on their own and give instructions on how to make certain weapons.

"These tips don't require a lot of training or a lot of weaponry," said Don Haider-Markel, political science professor at the University of Kansas. "... They just need a random person here and there who is sort of willing (to act)."