A week after the terrorist attack in San Bernardino, California that killed 14 people, FBI Director James Comey told a U.S. Senate hearing that the husband-wife team had been radicalized before they met over the internet and were married.

"They were talking to each other about jihad and martyrdom before they became engaged," said the FBI chief.

"We're working very hard to understand exactly their association and the source of their inspiration," Comey added.

The news that both Syed Farook and Tashfeen Malik had discussed attacks raised the unsettling issue of whether U.S. authorities somehow missed signs about Malik, and maybe Farook as well.

The date of their radicalization also suggests that they were motivated to take up arms before the rise of the Islamic State.

"We're working very hard to understand, did they have other plans, either for that day or earlier," The FBI Chief said at a previously scheduled Senate Judiciary Committee hearing.

Comey and other top officials will brief members of both the House and Senate behind closed doors on Thursday.

Discussing the tactics of the Islamic State, Comey said it's obvious that the group wants to get people into the United States to launch attacks, but again indicated that he is more worried about people being inspired here in the U.S.

"Do you believe ISIL cells are already here in America?" asked Sen. Lindsey Graham (R-SC).

"I don't have reason to believe that," Comey said.