Tashfeen Malik, a suspect in the San Bernardino massacre that killed 14 people and injured 21 others, posted a pledge of allegiance to ISIS on Facebook shortly after the rampage began.

Police say Malik and her husband, Syed Farook, attacked the County of San Bernardino Department of Public Health on Wednesday. The FBI is now investigating the shooting as "an act of terrorism," David Bowdich, the assistant FBI director in charge of the Los Angeles field office, said Friday. He said the FBI has uncovered evidence that has "led us to learn of extensive planning," including explosives and multiple armaments.

"We've also uncovered evidence that these subjects attempted to destroy their digital fingerprint," Bowdich said, noting that two "crushed" cell phones were found in a nearby trash can.

The shooting was first reported shortly after 11 am by the fire department, according to The Washington Post. The Facebook post, meanwhile, was uploaded at 11:15 am on Wednesday by an account with the alias Larki Zaat, according to a source close to the investigation. The account's profile picture did not feature a photograph, but rather had a logo with some writing on it.

Asked about the Facebook post, Bowdich acknowledged "there was a pledge of allegiance" but he declined to say how much it influenced the agency's decision to investigate terrorism as a motive, according to The New York Times. Facebook identified the post and removed the entire profile, which a spokeswoman said violated the company's community standards. "We don’t allow people to praise acts of terror or promote terrorism," she said. "We also work aggressively to ensure that we do not have terrorists or terror groups using the site."

This is not the first time Facebook has taken down an ISIS-related post from its site. In fact, social media companies like Facebook and Twitter have grappled in the past few years with how much they should monitor, and even remove, terrorist-related content on their respective services, especially as social media has become increasingly central to how ISIS supporters share propaganda and voice support.