Comey was echoing concerns he voiced to the Senate Homeland Security and Governmental Affairs Committee on Oct. 8.
"There is risk associated with bringing anybody in from the outside, but especially from a conflict zone like that," he told the Senate committee. "From the intelligence community's perspective, as I said, I think we've developed an effective way to touch all of our databases and resources to figure out what we know about individuals. … I don't think that's a cumbersome process. My concern there is that there are certain gaps."
He repeated that sentiment to the House Judiciary Committee on Oct. 22.
"We have gotten much better as an intelligence community at joining our efforts and checking our databases in a way that gives us high confidence. If we have a record on somebody, it will surface. That's the good news," Comey said. "The challenge we face with Syria is that we don't have that rich set of data. So even though we've gotten better at querying what we have, we certainly will have less overall. And so as I said to a question earlier, someone only alerts as a result of our searches if we have some record on them. That's the challenge we face with Syria."