"After reviewing Tashfeen Malik's immigration file, it is clear that immigration officials did not thoroughly vet her application," House Judiciary Committee chairman Bob Goodlatte said in a statement.
Malik, a 29-year-old Pakistani national, came to the United States last year on a fiancee visa, which Goodlatte said was issued despite a lack of proof that she had ever met her US-born husband, Syed Farook, 28.
Together the two shot dead 14 people and injured 22 at a social services center in San Bernardino, California earlier this month.
"The immigration official reviewing Malik's application requested more evidence to ensure the two met in person but it was never provided and her visa was approved anyway," Goodlatte said.
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He added that the only pieces of evidence provided to show that the couple had been in Saudi Arabia at the same time -- where they are said to have married -- were a statement by Farook and pages from their passports.
However, the exit month and date on Malik's passport was illegible, Goodlatte said, citing a translation provided by the Congressional Research Service.
"Even if Farook and Malik were in Saudi Arabia at the same time, this does not provide evidence that they met in person," Goodlatte said.
The Republican congressman accused President Barack Obama's administration of refusing to take necessary steps to fully vet visa applicants and said his committee was working on a bill "to strengthen visa processing security and protect national security."