The head of the U.S. Federal Bureau of Investigation says the two shooters in last week’s California massacre were radicalized before they met online and started discussing jihad and martyrdom about two years ago.

FBI Director James Comey told the Senate Judiciary Committee Wednesday that Syed Rizwan Farook and his wife, Tashfeen Malik, were radicalized “for quite a long time” before carrying the attack in San Bernardino, California.

The couple married last year.

Comey also said the two were inspired by foreign terrorist groups and described them as “homegrown violent extremists.”

“We’re working very hard to understand exactly their association and the source of their inspiration,” Comey said. “We’re also working very hard to understand whether there was anybody else involved with assisting them, with supporting them, with equipping them, and we’re working very, very hard to understand did they have other plans, either for that day or earlier, and that work continues.”

Comey said he was limited in what he could tell the committee because the investigation is continuing.

The FBI is looking into the attack as an act of terrorism, but there are no signs that the U.S.-born Farook and Malik, who was Pakistani, were part of a terror cell or group.

Last Wednesday, Farook and Malik killed 14 people and wounded 21 during a gathering of local government workers at a regional center in San Bernardino, California, east of Los Angeles.

They fled in a car and were gunned down in a shootout with police in a nearby residential neighborhood.

Malik had pledged allegiance to an Islamic State militant leader in a Facebook post, and Farook had contact with individuals linked to terror groups.

The guns used in the attack were bought legally by someone who police say is distantly related to Farook by marriage. So far he is not facing any charges.