The announcement that one of the two suspects in the Southern California rampage that left 14 dead had pledged her allegiance to the Islamic State group provides an indication of a possible motive for the commando-style attack. What is known so far:

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DOES THE ASSAULT HAVE A LINK TO TERRORISM?

The FBI announced Friday it is investigating the shooting as an act of terrorism. That does not mean the agency has concluded Syed Farook, 28, and his wife, Tashfeen Malik, 27, were terrorists — only that investigators have gathered enough preliminary information to move their probe in that direction.

That's a step beyond earlier this week, when police said they knew nothing conclusive about the possible motivation of Farook or his wife.

David Bowdich, assistant director of the FBI's Los Angeles office, said in Los Angeles Friday that the shooters attempted to destroy evidence, including crushing two cellphones and discarding them in a trash can.

The husband and wife used homemade explosives and assault-style rifles in the attack on a holiday party of Farook's co-workers, authorities say, but much remains unknown.

A U.S. law enforcement official said Friday that Malik, who later died with Farook in a gunfight with police, used an alias on Facebook to make her declaration of support for Islamic State and its leader. But there is no sign anyone from the group communicated with her or provided any guidance for the attack.

FBI Director James Comey noted the bureau's investigation so far has shown no evidence that the suspects were part of a larger group or members of a terror cell.

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WHO IS TASHFEEN MALIK?

In the days since the shooting, only sparse details have emerged about her life.

Farook told friends he met his future wife online and she was Pakistani. Malik arrived in the U.S. on a K-1 visa for fiancées and with a Pakistani passport in July 2014, authorities said.

The two were married Aug. 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; they left the baby with relatives Wednesday morning before the shooting.

Pakistani intelligence officials say Malik moved as a child with her family to Saudi Arabia 25 years ago. They say the family is originally from the Pakistani town of Karor Lal Esan, about 200 miles southwest of the capital of Islamabad in Punjab province.

Malik didn't stay in Saudi Arabia, eventually returning to Pakistan and living in the capital Islamabad, though she returned to Saudi Arabia for visits.

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ARE THERE ANY OTHER INDICATIONS OF A POSSIBLE TERRORISM LINK?

On Thursday, a U.S. intelligence official said Farook had been in contact with known Islamic extremists on social media.

But the official said the contact was with "people who weren't significant players on our radar" and dated back some time. There also was no immediate indication of any "surge" in communication ahead of the shooting.

Farook had no criminal record, and he and his wife weren't on the FBI's radar before the shooting. Also, police are looking at the possibility that the shooting was tied to a workplace dispute.

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HOW DID THEY AVOID DETECTION?

Family and friends have expressed disbelief that the quiet, religious couple staged the deadly attack.

Friends knew Farook by his quick smile, his devotion to Islam and his talk about restoring cars. They say they didn't know he was busy with his wife building pipe bombs and stockpiling thousands of rounds of ammunition for the assault on Farook's colleagues from San Bernardino County's health department.

The dead in Wednesday's attack ranged in age from 26 to 60, and 21 were injured.

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Abdollah reported from Washington. Associated Press writer Michael R. Blood contributed to this report.