From the Palm Beach Post via Daniel McAdams:

1:56 P.M. The global security firm G4S, with offices in Jupiter, has confirmed that Orlando shooter Omar Mateen has worked for the company since 2007. Statement from G4S:
“We are shocked and saddened by the tragic event that occurred at the Orlando nightclub. We can confirm that Omar Mateen had been employed with G4S since September 10, 2007. We are cooperating fully with all law enforcement authorities, including the FBI, as they conduct their investigation. Our thoughts and prayers are with all of the friends, families and people affected by this unspeakable tragedy.”
Related: More about G4S
1:28 p.m.: State records show a man named Omar Mateen is licensed as a security guard and also holds a firearms license. G4S, a global security firm with an office in Jupiter, listed an employee named Omar Mateen in a newsletter posted online. The company has not responded to requests to confirm whether its employee is the Orlando shooter.