WASHINGTON -- U.S. law enforcement officials said they are investigating the December 2 shooting at a California social services agency that killed 14 people and wounded 21 others as an act of terrorism.
Officials also said the woman who, along with her husband, is suspected of involvement in the massacre had pledged allegiance to the Islamic State militant group in social-media posts.
Police have identified the couple as Tashfeen Malik and her husband, Syed Farook.
FBI Director James Comey told reporters in Washington on December 4 that the probe had become a federal terrorism inquiry.
"The reason for that is that the investigation so far has developed indications of radicalization by the killers and of potential inspiration by foreign terrorist organizations," he said.
Comey said there were no indications that the couple was part of a terrorist cell or a network of terrorism.
He said neither were under investigation by the FBI and that even though one or both had had contacts with other individuals who were being investigated by the FBI, none were significant enough that they would have put the couple on the FBI's "radar screen."
Earlier, David Bowditch, assistant director for the FBI’s Los Angeles office, said investigators were looking at the "digital fingerprints" left on computers and elsewhere and that two partially destroyed cell phones had been recovered from trash cans not far from the scene of the shooting, at a social services agency in the city of San Bernardino, about 100 kilometers east of Los Angeles.
Officials say Malik and Farook used automatic weapons, handguns, and pipe bombs in the attack. Farook had attended the agency holiday party and then reportedly left agitated before returning with his wife, heavily armed and wearing tactical vests.
Authorities have said that the couple fired as many as 75 rounds into the room where the holiday party was being held before fleeing and they had more than 1,600 rounds left when they were killed.
Police later found 12 pipe bombs, tools to make more explosives and well over 4,500 rounds at the townhouse they were renting.
The couple was killed hours later after a car chase and a fierce gunbattle with police.
Malik was a Pakistani native who moved to the U.S. in 2014 on a fiancee visa. Farook, who was born in Chicago to Pakistani parents and raised in southern California, was a 28-year-old health inspector for the county.
Malik had been living in Saudi Arabia before marrying Farook two years ago.
Officials have said that while the killings may have been inspired by the Islamic State but there was no evidence that the radical group had directed the attack.
Meanwhile, other law enforcement official were quoted by news agencies and CNN as saying that Malik had pledged allegiance to the Islamic State group and its leader on Facebook.
The AP quoted an unnamed official as saying Malik made her posts under an alias and deleted them before she and Farook went on their rampage.
Another U.S. official was quoted as saying that Malik expressed "admiration" for the extremist group's leader on Facebook under the alias account.
But the official said there was no sign that anyone affiliated with the Islamic State communicated back with her, and there was no evidence of any operational instructions being conveyed to her.
Bowditch said neither Farook nor Malik was under prior investigation and he could not confirm the Facebook posting, saying investigators were still looking at it.
Saudi officials also said that Malik had not raised any red flags while she was living in Saudi Arabia.
The shooting has sparked heated debate in the United States about the wide availability of guns and the prevalence of mass shootings.
It also stoked fears that people who are radicalized or supportive of Islamic State could enter the United States alongside refugees from Syria or elsewhere.
The shooting was the deadliest in the United States since 2012.
A recently announced plan by the Obama administration to bring thousands more refugees from Syria’s civil war to the United States has been harshly criticized by many lawmakers and Republican presidential candidates.
Islamic State leaders, whose fighters have seized swaths of territory in Iraq and Syria as part of an effort to create a theocratic state called a caliphate, has urged sympathizers worldwide to commit violence in their countries.