The FBI is grappling with the aftermath of what a former Homeland Security counterterrorism coordinator calls one of its "great nightmares: someone they looked at who ultimately goes out and carries out a successful attack." The FBI—which investigated and cleared gunman Omar Mateen twice—also investigated but failed to stop Boston Marathon bomber Tamerlan Tsarnaev and Texas gunman Elton Simpson, leading some experts to say the agency is hampered by strict guidelines and limited resources, the Washington Post reports. The FBI's initial probe of Mateen, which began when colleagues at security firm G4S reported suspicious statements in 2013, took 10 months and involved phone surveillance, interviews, and the use of informants. It found no evidence of radicalization, but experts now wonder if more clues could have been found if more agents had been used.
The FBI is hampered not just by guidelines, but by the sheer volume of counterterrorism tips, with up to 10,000 investigations open at any one time, reports the New York Times. Sources say the agency is currently investigating more than 1,000 suspected "homegrown violent extremists," a task that involves thousands of agents and analysts. Authorities say they're trying to determine whether any leads were missed in the Mateen case. He was no longer on an FBI watch list when he bought the weapons used in the nightclub massacre, meaning the agency was not alerted, and Deputy Attorney General Sally Q. Yates says authorities are considering changing the system to ensure the FBI is notified when somebody previously investigated for terrorism links buys guns. (The FBI is considering charges against Mateen's wife, who may have known about the attack beforehand.)