Source: California Attacker Pledged Allegiance To ISIS

The female attacker in the deadly California shootings pledged allegiance to the leader of the Islamic State of Iraq and Syria online, a federal law enforcement source told CBS News.

The source confirmed to CBS News that Tashfeen Malik pledged her allegiance to ISIS leader leader Abu Bakr al-Baghdadi in an online posting, CBS News senior investigative producer Pat Milton reports.

The remarkable disclosure about Malik's online activities provided the first significant details suggesting a motive for her participation with her husband, Syed Farook, in the shootings that killed 14 people and wounded 21. Malik was a Pakistani woman who came to the U.S. in 2014 on a fiancee visa before Farook married her in California.

U.S. officials told CBS News that 28-year-old 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 her 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.