Last Updated Dec 4, 2015 11:07 PM EST
The source confirmed to CBS News that Tashfeen Malik pledged her allegiance to ISIS leader Abu Bakr al-Baghdadi in an online posting, CBS News senior investigative producer Pat Milton reports.
A law enforcement source told CBS News that Malik's Facebook posting was made under a fake name, Milton reports. The posting was published shortly before Wednesday's attack. The source said the pledge does not mean the attack was ordered or directed by ISIS.
A Facebook spokesperson confirmed to CBS News it "identified and removed the profile for violating our community standards."
"We don't allow people to praise acts of terror or promote terrorism," the spokesperson said. "We also work aggressively to ensure that we do not have terrorists or terror groups using the site."
Facebook is cooperating with law enforcement, according to the spokesperson.
Malik, 27, was a Pakistani who came to the U.S. in 2014 on a fiancee visa. Her husband, Syed Farook, a 28-year-old restaurant health inspector for the county, was born in Chicago to Pakistani parents and raised in Southern California.
The FBI has been investigating the shooting at a social service center as a potential act of terrorism but had reached no firm conclusions as of Thursday, with authorities cautioning repeatedly that the violence could have stemmed from a workplace grudge or a combination of motives.
FBI Director James Comey said Friday findings in a sweeping federal terrorism investigation into the shooting indicate the two suspects showed signs of radicalization but were not part of a broader network.
But Comey noted there's still "a lot evidence that doesn't quite make sense."
Comey said Farook and Malik didn't appear on the FBI's "radar screen" before the shooting Wednesday which left 14 people dead and 21 wounded, most of them county employees.
A source told CBS News that the pair were looking at ISIS propaganda online.
Two law enforcement sources told CBS News that Farook had been in contact with an individual in the U.S. with suspected ties to terrorism who was known to the FBI, Milton reports. According to the sources, Farook was also in communication with people overseas who have links to terrorism.
The sources told CBS News that investigators are focused on Farook's domestic and overseas contacts to try to determine to what extent he was influenced by those individuals, Milton reports.
U.S. officials told CBS News that Farook started searching for a wife using an online dating website. He met Malik, and they became engaged in 2013 after he traveled to Saudi Arabia during the annual pilgrimage known as the hajj.
Farook returned to Saudi Arabia in July 2014 to bring Malik to the U.S. She passed a Homeland Security counterterrorism screening as part of the vetting process, and officials told CBS News Farook was not on any U.S. terror watchlists.
Christian Nwadike was shocked when he learned the man accused of gunning down over a dozen people turned out to be the coworker he sat only feet from for nearly four years. He said Farook was different after he returned from Saudi Arabia.
"Do you believe that he was radicalized?" CBS News correspondent David Begnaud asked him.
"Yes, by the wife, I think he married a terrorist," Nwadike said.
"He married a terrorist?" Begnaud asked.
"Yes, he was set up through that marriage," Nwadike said.
Law enforcement officials have long warned that Americans acting in sympathy with Islamic extremists - though not on direct orders - could launch an attack inside the U.S. ISIS in particular has urged sympathizers worldwide to commit violence in their countries.
Farook had no criminal record and was not under scrutiny by local or federal law enforcement before the attack, authorities said. Friends knew him by his quick smile, his devotion to Islam and his talk about restoring cars.
They didn't know he was busy with his wife building pipe bombs and stockpiling thousands of rounds of ammunition for the commando-style assault Wednesday on a gathering of Farook's colleagues from San Bernardino County's health department.
"This was a person who was successful, who had a good job, a good income, a wife and a family. What was he missing in his life?" asked Nizaam Ali, who worshipped with Farook at a mosque in San Bernardino.
Authorities said that the couple sprayed as many as 75 rounds into the room before fleeing and had more than 1,600 rounds left when they were killed. At home, they had 12 pipe bombs, tools to make more explosives and well over 4,500 rounds, police said.
Police Lt. Mike Madden, one of the first officers to reach the room, said the carnage was unspeakable, the scene overwhelming: the smell of gunpowder, the wails of the wounded the blood, fire sprinklers going off and fire alarms blaring. All in a room with a Christmas tree and decorations on every table.
The dead ranged in age from 26 to 60. Among the 21 injured were two police officers hurt during the manhunt, authorities said. Two of the wounded remained in critical condition Thursday. Nearly all the dead and wounded were county employees.
They were remembered Thursday night as several thousand mourners gathered at a ballpark for a candlelight and prayer vigil with leaders of several religions.
The soft-spoken Farook was known to pray every day at San Bernardino's Dar Al Uloom Al Islamiyah mosque. That is where Nizaam Ali and his brother Rahemaan Ali met Farook.
The last time Rahemaan Ali saw his friend was three weeks ago, when Farook abruptly stopped coming to pray. Rahemaan Ali said Farook seemed happy and his usual self. Both brothers said they never saw anything to make them think Farook was violent.
They said Farook reported meeting his future wife online.