Female shooter Tashfeen Malik swore allegiance to ISIS

Tashfeen Malik, the female gunman in the San Bernardino massacre, posted a note on Facebook pledging allegiance to ISIS leader Abu Bakr al-Baghdadi, three U.S. officials familiar with the investigation told CNN.

Malik allegedly posted under a different account name, either during or before the deadly attacks. The report comes via several federal officials who've investigated the electronic devices the attackers used.

There is also a "very serious" possibility that 27-year-old Malik, the mother of a six-month-old who left the child with relatives and took up arms, along with her husband Syed Farook, and killed 14 people and wounded 21 at a Christmas party for county employees in San Bernardino, was the one who radicalized her spouse, Fox News reports investigators suspect.

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The cable outlet cited unnamed federal investigators in reporting that the two also planned a second attack but were confronted – and killed – by police before they could carry that out. At one point as the couple attempted to elude police, Malik fired an assault rifle out the back window of their sport utility vehicle at pursuing officers.

"A U.S. official confirmed to Fox News that the two met and became engaged after [Syed] Farook traveled to Saudi Arabia in September 2013. Malik, a Pakistani citizen, applied for a K-1 visa at the American embassy in Islamabad in May 2014 and Farook traveled to Saudi Arabia that July to bring her to the U.S. After a background check by the FBI and the Department of Homeland Security, she was granted a conditional green card last summer.

"The Saudi Embassy in Washington has confirmed that Farook's 2014 trip lasted nine days," Fox reported.

They were married Aug. 16, 2014, and both listed their religion as Muslim.

Syed Farook

Two brothers who attended the same Southern California mosque as Farook say he was a devout Muslim who showed up to pray every day for two years before he abruptly stopped three weeks ago, according to the Associated Press.

Nizaam Ali and Rahemaan Ali said Thursday Farook had recently memorized the Quran.

Ali said he had met Malik on a few occasions, but she wore a head scarf that obscured her face, reports the Los Angeles Times.

“If you asked me how she looked, I couldn’t tell you,” Ali said.

They died in a firefight with police in San Bernardino about four hours after they reportedly stormed into a party for county workers with multiple weapons and killed 14.

The victims were identified as Benneta Betbadal, 46; Robert Adams, 40; Nicholas Thalasinos, 52; Isaac Amanios, 60; Aurora Godoy, 26; Larry Kaufman, 42; Michael Wetzel, 37; Shannon Johnson, 45; Harry Bowman, 46; Yvette Velasco, 27; Sierra Clayborn, 27; Tin Nguyen, 31; Juan Espinoza, 50; and Damian Meins, 58.

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Another 21 were injured, and authorities have described how the duo had thousands of rounds of ammunition with them when they were killed, as well as thousands more in their home, where investigators also found pipe bombs.

Investigators said the duo tried to erase their digital fingerprints before the attack, destroying cell phones and computer drives.

Fox reported investigators believe that the husband or wife was in contact with suspected al-Qaida terrorists during a trip to Saudi Arabia.

That's despite the fact she had passed a Department of Homeland Security counterterrorism screen on her arrival in the U.S.

"Law enforcement sources told Fox News late Thursday that there was a 'very strong' possibility that Malik functioned as Farook's terror trainer and may have even put together pipe bombs found by authorities at the various crime scenes Wednesday," Fox reported. The detonator from a pipe bomb found at the murder scene was reportedly fashioned with a remote-control toy, as suggested by al-Qaida's online magazine, Inspire, and likely used in the Boston Marathon bombs. Police found in their home a dozen more pipe bombs, which were also  identical to those the magazine depicted, along with step-by-step instructions on “How to Build a Bomb in the Kitchen of Your Mom.”

Farook, 28, and Malik sprayed a room at the Inland Regional Center with bullets after it had filled up with about 75 of Farook's co-workers, including one with whom he argued just weeks before about whether Islam was actually a peaceful religion.

Among the many questions still to be answered is how the duo obtained more than $30,000 worth of guns and explosives.