What follows is a brief excerpt from Kim Zetter's 6-17-16 Wired article entitled "How Does the FBI Watch List Work? And Could It Have Prevented Orlando?":
"OF ALL THE details investigators have uncovered about Orlando terrorist Omar Mateen, perhaps the most infuriating is the fact that he spent 10 months on a government watch list, yet had no trouble buying an assault rifle and a handgun.
"Authorities placed Mateen on a watch list in May 2013 after coworkers at the Florida courthouse where he was a security guard told authorities he boasted of connections to al Qaeda and other terrorists organizations. He remained on the list for 10 months, and FBI Director James Comey told reporters this week that during that time the agency placed Mateen under surveillance and had confidential sources meet with him.
"But the feds removed Mateen from the list in March 2014, after concluding that he had no significant links to terrorism beyond attending the same mosque as an American suicide bomber who died in Syria. 'We don’t keep people under investigation indefinitely,' Comey said, adding that he doesn’t see anything that his agents should have done differently.
"Comey didn’t identify the list Mateen was on, but an unnamed official told the Daily Beast that he was in two databases, the Terrorist Identities Datamart Environment database and the Terrorist Screening Database, more commonly called the terrorist watch list.
"Here’s a look at what the lists are and how someone gets their name on one."