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ORLANDO, FLORIDA - JUNE 12:  FBI agents seen outside of Pulse nightclub after a fatal shooting and hostage situation on June 12, 2016 in Orlando, Florida. The suspected shooter, Omar Mateen, was shot and killed by police. 50 people are reported dead and 53 were injured. (Photo by Gerardo Mora/Getty Images)
ORLANDO, FLORIDA - JUNE 12:  FBI agents seen outside of Pulse nightclub after a fatal shooting and hostage situation on June 12, 2016 in Orlando, Florida. The suspected shooter, Omar Mateen, was shot and killed by police. 50 people are reported dead and 53 were injured. (Photo by Gerardo Mora/Getty Images)

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    Orlando gunman Omar Mateen was on FBI radar

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Orlando gunman Omar Mateen was on FBI radar

The FBI investigated Omar Mateen before he carried out the worst mass shooting in the U.S., killing 49 people at Pulse nightclub in Orlando, Florida. CNN's Pamela Brown reports.

Orlando gunman Omar Mateen was on FBI radar

The FBI investigated Omar Mateen before he carried out the worst mass shooting in the U.S., killing 49 people at Pulse nightclub in Orlando, Florida. CNN's Pamela Brown reports.