(ORLANDO, Fla.) -- Omar Mateen, a 29-year-old U.S.-born citizen, has been identified as the suspect in Sunday's mass shooting that left at least 50 dead and more than 50 others wounded at the Pulse Orlando, a gay nightclub in Orlando, Florida.
In the midst of the attack, Mateen called 911 and pledged his allegiance to ISIS, according to two law enforcement officials.
Terrorism observers told ABC News that ISIS supporters have cheered the massacre online and an ISIS communique referred to the shooter as an ISIS "fighter," but no evidence has yet appeared that ISIS directed or had prior knowledge of the attack.
ISIS, which is based in Syria, has targeted gay men for beatings and murder in the Middle East and has filmed its members throwing some men suspected of being gay from the roofs of buildings.
During Mateen's 911, he also made reference to the 2013 Boston Marathon bombers, Tamerlan and Dzhokhar Tsarnaev, officials said.
Law enforcement officials told ABC News that Mateen was "on the radar" of U.S. security officials for some time but was not the target of a specific investigation. Mateen, whose parents are from Afghanistan, was born in New York but lived in an apartment in Fort Pierce, Florida, more than 100 miles from Orlando, officials said.
Public records show Mateen was divorced in 2011 and his ex-wife said Sunday he was violent, mentally unstable and beat her repeatedly when they were married. The woman said she met Mateen online about eight years ago and moved to Florida to marry him, as first reported by The Washington Post.
“He was not a stable person,” the ex-wife said, according to the Post. “He beat me. He would just come home and start beating me up because the laundry wasn’t finished or something like that.”
Officials said Mateen had two firearms licenses, a security officer license and a statewide firearms license, all expiring in September 2017. Mateen worked for the security firm G4S since 2007, the company said, adding that it is cooperating fully with law enforcement.
Copyright © 2016, ABC Radio. All rights reserved.