Omar Mateen has been identified as the Pulse nightclub gunman who killed 20 people during a rampage Sunday morning, CBS reported.

Mateen, 29, was a U.S. citizen from Port St. Lucie, Fla., the network added.

He was killed after a showdown with police inside the nightclub. His parents are from Afghanistan and authorities are investigating whether he had ties to Islamic extremists, CBS said.

Florida Department of Law Enforcement Special Agent in Charge Danny Banks says the mass shooting is being investigated as an act of terrorism.

He says authorities are looking into whether this was an act of domestic or international terror, and if the shooter was a lone wolf.

Orlando Police Chief John Mina says the shooter was armed with an assault-type rifle, a handgun and some type of suspicious device.

Police had said previously on Twitter that there was a “controlled explosion” at the scene of the shooting at Pulse Orlando. Mina says that noise was caused by a device intended to distract the shooter.

• Material from The Associated Press was used in this report.

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