The Orlando gunman pledged allegiance to the Islamic State during a 911 call he made during the attack that left 50 dead so far, officials said.
According to reports, Omar Mateen also referenced the Boston Marathon bombings in the phone call he made to emergency dispatchers after 2 a.m. on Sunday.
Authorities believe Mateen, an American born son of two immigrants from Afghanistan, took an AR-15 style weapon into the nighclub as well as a handgun he'd purchased just days earlier.
Fifty people were killed in the attack.
Of the additional 50-plus people Mateen is believed to have killed, "many" were considered to be in critical condition.
Police say Mateen was shot and killed by police three hours into the ordeal, which reportedly began in the Pulse parking lot.
After a police officer engaged with the suspect, he went inside Pulse, creating a hostage situation. The shooter reportedly had an AR-15 style weapon as well as a handgun.
Authorities managed to save about 30 people by crashing through a wall in an armored vehicle.
The incident is being investigated as a domestic terror event.