The FBI said Friday they are investigating the San Bernardino massacre as an "act of terrorism."
The suspects, Tashfeen Malik and Syed Rizwan Farook, crushed their cellphones and tried to erase their digital fingerprints, FBI Los Angeles Assistant Director in Charge David Bowdich said.
"There are a number of pieces of evidence that have pushed us off the cliff to say that this is now an act of terrorism," he said.
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Malik posted a statement of support for ISIS leader Abu Bakr al-Baghdadi on Facebook, law enforcement sources told NBC News on Friday.
One official familiar with the issue said Malik, 27, posted the statement "just before the attack."
But FBI Director James Comey said later on Thursday that there was no indication that Farook or Malik were part of an organized terror cell or group, and that their activity up until the shooting didn't raise any red flags for investigators.
"There's a lot of evidence in this case that doesn't quite make sense," Comey said.
A Facebook official told CNBC that the social media site flagged and removed Malik's profile after the attack for violating community standards, as Facebook does not allow users to praise terror acts or promote terrorism. Facebook said no one had reported Malik's account. The social media network is cooperating with law enforcement.
Bowdich said the FBI is aware of Malik’s purported Facebook post about ISIS and is looking into it, but so far, there is no confirmed link to the terror group.
“We know they were in telephonic conversations with people here in the U.S.," Bowdich said.
Investigators are looking into whether Malik, a Pakistani who spent most of her childhood in Saudi Arabia, was a radicalizing influence on Syed Rizwan Farook. Farook, a 28-year-old restaurant health inspector for the county, was born in Chicago to Pakistani parents and raised in Southern California.
Reuters reported that Pakistani intelligence has contacted Malik's relatives about Wednesday's mass killing. Malik, who is from the Layyah district in the Punjab province, returned to her homeland five of six years ago to study pharmacy at the Bahauddin Zakariya University in the city of Multan, according to Reuters.
Documents obtained by NBC News Thursday show that the garage at the suspects' residence in Redlands, California, "was set up as a bomb making facility including metal working equipment."
Investigators found elbow pipes, internal plugs and caps for the pipes, tape, wiring, wire strippers and cutters, a soldering gun and an electric drill. There was also at least one container of smokeless power and a number of miniature of Christmas tree lights with green insulated wire, NBC News reported.
A search of their vehicle also yielded other materials, including copper pipe rigged with a pull string initiator, a variety of powders and powder filler, batteries and a remote control transmitter.
The materials have not undergone a full lab examination, according to NBC News.
Bowdich said Farook was not under active surveillance and there was no investigation pending on him.
“There are no other suspects currently under arrest," Bowdich said. "It is possible there may be some in the future. We don’t know.”
Bowdich urged the San Bernardino community to go about their daily business and said the FBI is not aware of any further threats.
"Do not let this cause mass hysteria," he said. "We’re not there. We’re not there at all.”
San Bernardino County Sheriff John McMahon echoed Bowdich's comments and asked the public to remain vigilant.
Eric Jankiewicz contributed to this report.