Omar Mateen, the 29-year-old identified as the shooter who massacred at least 49 people at the popular gay Pulse nightclub in Orlando early Sunday, was an ISIS sympathizer upset by two gay men openly kissing and touching in front of his family.
Investigators are now trying to determine whether it was terrorism, a hate crime or a combined force of both triggers that pushed the man who lived in a modest two-bedroom condominium in Fort Pierce, Florida, over the edge.
His father, Seddique Mir Mateen told NBC News that "this had nothing to do with religion" but felt it was likely triggered by an encounter with two gay men a few months ago.
"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 said. "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," Mateen's father said. "We weren't aware of any action he is taking. We are in shock like the whole country."
Despite his father's declaration that the shooting had nothing to do with his Islamic faith, in 2013 Mateen was interviewed twice by federal agents after co-workers reported that he made "inflammatory" comments to them about radical Islamic propaganda. He was also investigated by the FBI again the following year because of ties with an American who traveled to the Middle East to become a suicide bomber.
Law enforcement sources also told NBC News that Mateen swore allegiance to the leader of ISIS, Abu Bakr al-Baghdadi, in a 911 call just moments before his killing spree at Pulse.
Prior to the shooting that rocked America on Sunday, Mateen, who was killed by a SWAT team, appeared to live a relatively quiet life, according to The Washington Post.
He worked as a security guard and showed a strong interest in law enforcement, even once sharing with friends about becoming a police officer. The New York native appears in a series of Myspace photos wearing New York Police Department shirts. He held a permit to carry a concealed weapon, according to Florida records.
According to The Washington Post Mateen also showed early signs of a violent temper.
"He was not a stable person," Sitora Yusifiy, who was briefly married to Mateen, told the paper. "He beat me. He would just come home and start beating me up because the laundry wasn't finished or something like that."
Yusifiy told the Post she met Mateen through an online dating service and eventually agreed to move to Florida to be with him. The two married in March 2009 and moved into the Fort Pierce condo that Mateen's family owned.
"He seemed like a normal human being," Yusifiy, who divorced Mateen in 2011, said.
She further revealed that her ex-husband was very private and preferred to spend his free time at the gym. There were no signs, she said, that he had fallen under the influence of radical Islam.
One friend who did not wish to be named, however, told The Washington Post that Mateen became increasingly more religious after he divorced Yusifiy. He even went on a religious pilgrimage to Saudi Arabia.
"He was quite religious," said the friend.
Mateen also regularly attended the Islamic Center of Fort Pierce and was there as recently as two days ago, Imam Shafiq Rahman said on Sunday.
Mateen's father and young son would pray with him, and Mateen's three sisters were active volunteers at the mosque which had about 150 congregants, Rahman told the Post.
"He was the most quiet guy; he never talked to anyone," Rahman said. "He would come and pray and leave. There was no indication at all that he would do something violent."