Nuclear security

Security Firm That Employed Orlando Gunman Guards U.S. Nuclear Sites

The security firm that employed the Orlando gunman behind the worst mass-shooting in U.S. history says it's guarded "90 percent of U.S. nuclear facilities" – raising concern that would-be terrorists could easily gain inside access to the most sensitive sites on American soil and release untold devastation.

Omar Mateen, who slaughtered 49 people early Sunday at a popular gay nightclub and pledged allegiance to the Islamic State group, worked as a guard for G4S, an enormous multinational security firm that's previously faced scrutiny for safety and management lapses.

Mateen, who was killed in a shootout with police, was employed at a "residential community in South Florida," not a nuclear site, the company said in a statement. Nonetheless, nuclear safety and private security experts say his employment at G4S – which included an initial background check when he was recruited in 2007 and another in 2013, according to the company – highlights potential vulnerabilities at the nation's nuclear sites, especially in light of successful break-ins and apparent sabotage in the past four years alone.