Mother of San Bernardino shooter being looked at by FBI

On Sunday, Attorney General Loretta Lynch said the FBI is conducting an investigation into what, if anything, the mother of San Bernardino shooter Syed Farook knew about the stockpile of ammunition and bombs being stored in the home she shared with him and his wife.

"Obviously, it's something that we're looking at very, very closely," Lynch said on Meet the Press. Law enforcement officials say Rafia Farook lived in a Redlands, California, townhouse with Farook and his wife, Tashfeen Malik. Following the shooting, authorities raided the house and found at least 15 pipe bombs under construction and thousands of rounds of ammunition. Lynch said that 300 people have been interviewed and numerous searches conducted, and investigators "do not have evidence that they were part of either a larger group or cell, or that they were planning anything else."

Investigators also say the pair carried two .223-caliber rifles that were originally purchased in 2011 and 2012 by Farook's former neighbor and friend, and they do not yet know how the rifles were transferred to Farook and Malik. That man is not a suspect, officials said, and NBC News reports he has checked himself into a mental health facility.