The Orlando gunman responsible for the deadliest shooting in American history cleared background checks at global security firm G4S, where he worked, twice.
Omar Mateen was employed by the company for nine years as an armed guard for a gated retirement community in South Florida.
The latest background check carried out by the firm - which he passed - was in 2013, G4S said.
Employees at a gun shop refused to sell Omar Mateen bulk ammunition because he was acting suspiciously.
The Orlando mass shooting - the worst in modern US history - has reignited the gun control debate in America.
Omar Mateen is said to have called Orlando's News 13 about 45 minutes after the shooting at the Pulse nightclub began.