The shooter suspected for killing at least 50 people and injuring more than 53 others in a gay nightclub in Orlando has been identified as Omar Seddique Mateen.
Omar, 29, a New York-born Florida resident and U.S. citizen who was the son of immigrants from Afghanistan had twice been questioned by FBI agents in recent years, authorities said.
But, in both cases, the FBI determined Mateen was not a threat and closed the investigations.
Mateen's former wife Sitora Yusufiy, described him as emotionally and mentally disturbed with a violent temper. She said she had been beaten and otherwise physically abused by Mateen during outbursts in which he would "express hatred towards everything".
She was "rescued" by family members just four months into a stormy marriage that began in 2009 and ended in divorce, she said.
"He hardly had any friends," Syed Shafeeq Rahman, who heads the Islamic Center of Fort Pierce, told Reuters. "He would come with his little son at night to pray and after he would leave."
Yusufiy said Mateen desperately wanted to be a policeman and hung out with a lot of cops, often going to the shooting range with them.He also worked as an armed guard for the security firm G4S, the world's largest, according to the company.
As the shooting rampage was unfolding, Mateen "made calls to 911 this morning in which he stated his allegiance to the leader of the Islamic State," said Ronald Hopper, the FBI's assistant special agent in charge on the case.
Officials also said he purchased two weapons, a handgun and "long gun," just in the past few days.
"So far as we know at this time, his first direct contact was a pledge of bayat (loyalty) he made during the massacre," said a U.S. counterterrorism official. "This guy appears to have been pretty screwed up without any help from anybody."
The attacker was carrying an AR-15-style assault rifle and a handgun, Orange County Sheriff Jerry Demings said. He also had an unidentified "device," said Orlando Police Chief John Mina.
The suspect's father, Mir Seddique, sometimes cited as Seddique Mir Mateen, told NBC News on Sunday that his son had recently expressed anti-gay sentiments and had become angry when he saw two men kissing a few months ago in Miami. He said the attack "had nothing to do with religion."
This attack has been ranked as the deadliest single U.S. mass shooting incident, eclipsing the massacre of 32 people at Virginia Tech University in 2007.
(With Reuters inputs)