Attorney General Loretta Lynch said Sunday that the FBI is looking into whether the mother of one of the attackers in the San Bernardino, California, shootings knew about the criminal activities of her son and his wife.
"Obviously, it's something that we're looking at very, very closely," Lynch said on NBC's "Meet the Press."
Law enforcement officials have said that Rafia Farook lived in the same house in Redlands, California, where her son, Syed Farook, and his wife, Tashfeen Malik, were building at least 15 pipe bombs and stockpiling thousands of rounds of ammunition.
Farook and Malik were carrying two .223-caliber rifles — a Smith & Wesson M&P 15 and a DPMS model — which were originally purchased in 2011 and 2012 by a friend of Farook's who was also a neighbor.
Investigators said don't know how the rifles were transferred to the couple before they stormed the Inland Resource Center, a social services agency where dozens of people were gathering for a holiday party.
Officials say the man isn't a suspect in the shootings and that he was distraught afterward. Two law enforcement officials said the man checked himself into a mental health facility in Southern California.
Senior law enforcement officials also said Sunday that they do not yet know whether the terrorist group ISIS specifically played a significant role in the couple's radicalization.
Another official said there's still no evidence that the couple was in direct contact with any terror groups or individuals overseas leading up to the attack.
The Italian newspaper La Stampa reported Sunday that Farook's father, also named Syed, said that his son agreed with the goal of ISIS leader Abu Bakr al Baghdadi to create an Islamic state.
U.S. officials have said that around the time of the San Bernardino shooting attack, Malik sent a post to her Facebook page pledging loyalty to al Baghdadi.
A representative of the newspaper told NBC News that the father said he had been interviewed by the FBI for seven hours.
On "Meet the Press," Attorney General Lynch said the pattern of people in the United States becoming radicalized by a terrorist group's propaganda has become a familiar one.
But as for the couple that committed last week's mass shooting, "We're not sure which one (fanatical ideology) they picked in this case, despite the media accounts."
Lynch said that after conducting 300 interviews and carrying out several searches, investigators "do not have evidence that they were part of either a larger group or cell, or that they were planning anything else."
Rep. Michael McCaul, R-Texas and chairman of the House Homeland Security Committee, said he's been told that federal investigators are working hard to determine what Malik was doing overseas before she came to the U.S. in 2014 to be Farook's wife.
"There's a serious investigation ongoing into what she was doing in Pakistan and in Saudi, including if she attended the red mosque in Islamabad, which is a very radicalized mosque," he said on "Fox News Sunday."