From Texas Standard:
According to reports, the Orlando gunman Omar Mateen had been questioned by the FBI twice – in 2013 and 2014. But yet, he wasn't on their watch list.
Paul Miller, associate director of the Clements Center for National Security at the University of Texas at Austin, says the FBI's internal processes are fairly opaque.
"I'm not convinced they are very consistent from case to case either," he says. "The FBI handles a very large caseload, they go through these things all the time. They can't afford to put everyone on the watch list."