Tashfeen Malik, who along with her husband killed 14 people in Southern California, reportedly passed three background checks by American officials before she moved from Pakistan to the United States and none of them found her social media posts about jihad.
The New York Times reports U.S. law enforcement officials discovered old and previously unreported postings as they investigated Malik and her husband Syed Rizwan Farook.
The applicants are subject to a vetting process that includes at least one in-person interview, fingerprints, checks against U.S. terrorist watch lists and reviews family members, travel history and places where a person has lived and worked.
Foreigners applying from countries recognized as home to Islamic extremists, such as Pakistan, undergo additional scrutiny before the State Department and Homeland Security Department approve permission for a visa.