SAN BERNARDINO - A U.S. intelligence official says one of the shooters who killed 14 people in California had been in touch on social media with extremists who are under FBI scrutiny.

The official would not further describe the contacts by Syed Rizwan Farook. He would not be quoted because he was not authorized to discuss the matter publicly.

The official says investigators are still trying to determine whether and how he became radicalized and whether he was in contact with any foreign terrorist organization.