While authorities begin the pain-staking work into why gunman Omar Mateen massacred at least 50 people at a popular gay nightclub in Florida, they'll have a number of clues for understanding the mindset of the mass murderer.
A few key revelations about his past came to light hours after the 29-year-old was identified as the shooter who took the Pulse Nightclub in Orlando hostage early Sunday before he was killed by a SWAT team. Now, law enforcement are trying to determine whether terror, hate or both pushed him over the edge.
- His father told NBC News his son was enraged after recently seeing a same-sex couple kissing in front of his family, an event that could have set him off.
- In 2013, Mateen was interviewed twice by federal agents after coworkers reported that he made "inflammatory" comments to them about radical Islamic propaganda. The following year, the FBI looked at him again because of ties with an American who traveled to the Middle East to become a suicide bomber.
- Law enforcement sources told NBC News he swore allegiance to the leader of ISIS, Abu Bakr al-Baghdadi, in a phone call to 911 moments before the rampage at Pulse.
- There's no indication that Mateen was in touch with terrorists overseas or that the attack was directed by someone else, a law enforcement officials told NBC News. Nor is there evidence that anyone helped or encouraged him, several officials said.
With that information, investigators are looking into whether religious extremism motivated the attack and are piecing together what triggered Mateen, who lived roughly two hours south of Orlando in Fort Pierce and worked as a security guard.
Mateen didn't appear to have any direct ties with ISIS, sources said, although he was a follower of ISIS propaganda and referenced the Tsarnaev brothers, who carried out the Boston Marathon bombings in 2013, at the scene of the shooting.
But while law enforcement delves into what may have radicalized Mateen, who was born in New York and lived in Florida for at least the past decade, his family believes he was fueled by pure hate against the LGBT community.
His father told NBC News that his son was affected by a recent incident involving two men showing each other affection.
"We were in Downtown Miami, Bayside, people were playing music. And he saw two men kissing each other in front of his wife and kid and he got very angry," Mateen's father, Seddique Mir Mateen, told NBC News on Sunday. "They were kissing each other and touching each other and he said, 'Look at that. In front of my son they are doing that.' And then we were in the men's bathroom and men were kissing each other."
"We are saying we are apologizing for the whole incident," the elder Mateen said. "We weren't aware of any action he is taking. We are in shock like the whole country."
He added: "This had nothing to do with religion."
Driving the point home that religion was a consideration in the mind of investigators, at a 10:30 a.m. news conference Saturday, officials brought a member of the Muslim community to speak.
Police did not explicitly say Mateen was Muslim, but Islamic groups put out statements denouncing the carnage.
"We condemn this monstrous attack and offer our heartfelt condolences to the families and loved ones of all those killed or injured. The Muslim community joins our fellow Americans in repudiating anyone or any group that would claim to justify or excuse such an appalling act of violence," the Council on American-Islamic Relations Orlando Regional Coordinator Rasha Mubarak said in a statement.
Seddique Mir Mateen said his son was a husband and father to a 3-year-old son. He worked in security and attended Indian River State College. A spokeswoman said he got an associate of science degree in criminal justice technology in 2006.
His job in security, meanwhile, gave him access to his weapons; police say he used a handgun and AR-15-type rifle in the shooting spree.
ATF officials tweeted Sunday that he legally purchased the firearms within the last week.
Records also show he had filed a petition for a name change in 2006 from Omar Mir Seddique to Omar Mir Seddique Mateen.
An ex-wife of Mateen told The Washington Post that he was prone to violent behavior and beat her. They had met online eight years ago and she moved to Florida to be with him.
"He was not a stable person," the unidentified ex-wife said. "He beat me. He would just come home and start beating me up because the laundry wasn't finished or something like that."
She said his family was originally from Afghanistan and confirmed pictures posted online on Myspace were of Mateen, some in which he wore shirts with the NYPD logo. In one selfie, he rubs his hands on his chin and tilts his head.
The marriage lasted only months, but during that time she never noticed him becoming radicalized. Still, she lived in fear. Her parents came to take her away and the couple officially divorced in 2011.
"He was a very private person," the ex-wife said.
Rep. Alan Grayson, D-Fla., whose district includes the area of the massacre, suggested to reporters that "more likely than not" the shooting spree at the nightclub was ideologically motivated.
"Let me put it this way," he said, "the nationality of family members is indicative."
A family friend told NBC News that Mateen's parents have always been "very respectful" of America, and the idea that someone in the family would unleash terror is surprising.
"They are a beautiful close-knit-loving family and they have no hate for anyone and they are upset as anyone about what happened and feel for the victims," said Desiree Mufson.