Story highlights

Tashfeen Malik advocated jihad in messages on social media

Her comments were made under a pseudonym and with strict privacy settings

Authorities are working to trace the electronic trail of Malik and her husband

CNN  — 

Tashfeen Malik advocated jihad in messages on social media, but her comments were made under a pseudonym and with strict privacy settings that did not allow people outside a small group of friends to see them, U.S. law enforcement officials told CNN on Monday.

Malik and her husband, Syed Rizwan Farook, opened fire on the latter’s co-workers at a work event on December 2 in San Bernardino, California, killing 14.

Authorities are working to trace the electronic trail of the killers and trying to find out whom they interacted with, how they hatched and carried out the plot, and why.

The New York Times reported on Sunday that U.S. immigration officials conducted three background checks on Malik when she emigrated from Pakistan but allegedly did not uncover social media postings in which she said she supported violent jihad and wanted to be a part of it.

According to the law enforcement officials, because Malik used a pseudonym and privacy controls, her postings would not have been found even if U.S. authorities had reviewed social media as part of her visa application process.

A U.S. official told CNN shortly after the San Bernardino attack that the United States only recently began reviewing the social media activity of visa applicants from certain countries. The date that these types of reviews began is not clear, but it was after Malik was considered, the source said.

Visa vetting process: ’100% security difficult to achieve’

In addition to tracing what the killers said online, investigators have been working with various cell phones found either near or at the couple’s home. So far, the FBI hasn’t been able to recover data from two smashed cell phones found near the couple’s home.

They were able, however, to retrieve some data from two other phones found at the shooters’ home. Metadata showed that on the day of the attack the killers visited a park, which was the scene of an intensive lake search by FBI divers that finished over the weekend.

The search yielded nothing useful to the investigation, said a law enforcement source.

CNN’s Faith Karimi and Ana Cabrera contributed to this report.