The FBI says they are working to fill an 18-minute gap in the timeline of the mass shooting in San Bernardino last month. Fourteen people were killed in the attack on the Inland Regional Center.

At a press conference, David Bowdich, the assistant director in charge of the FBI's Los Angeles office, said they have accounted for three hours and 42 minutes of the shooters' time. That's after executing 29 search warrants and conducting more than 550 interviews, law enforcement officials say.

They haven't been able to account for the whereabouts of Syed Farook and his wife Tashfeen Malik after the attack, between 12:59 p.m. and 1:17 p.m. on Dec. 2. The couple were shot dead by police who caught up with them that afternoon.

"So why is that 18 minutes so important? It's important because we want to ensure that we know whether they stopped at any locations, any residence, and any businesses that we don't already know about," Bowdich says. "We want to ensure if they made contact with anyone that we don't already know about between those hours, or between that time, that we're able to fully investigate those matters."

Copyright 2016 NPR. To see more, visit