FORT PIERCE, Fla. (AP) – Like many other young American men, Omar Mateen worked a series of unremarkable jobs after finishing vocational high school – a Publix grocery store, Circuit City, Chick-Fil-A and Walgreens.

He graduated in 2003 and jumped through a series of jobs related to nutrition and health, working at Nutrition World, Gold’s Gym and a GNC store.

An early marriage faltered. But eventually he found some form of stability with a job as a security guard in South Florida, where he was still working when he stormed a gay nightclub early Sunday in Orlando, resulting in the deaths of 49 people and the wounding of 53 more. He died in a gunfight with police.

Mateen, 29, spent most of his childhood on Florida’s Atlantic coast and lived there as an adult, not far from his parents. Born in the New York City borough of Queens in 1986, he moved with his family to the Long Island town of Westbury two years later and then in 1991 to Port Saint Lucie, Florida, about 125 miles southeast of Orlando.

Imam Syed Shafeeq Rahman of the city’s Islamic Center said he knew Mateen and his family since the shooter was a boy and never saw any signs of violence in him. The Orlando attack, he said, “was totally unexpected.”

But one colleague at the security contractor G4S, his most recent company, remembered the son of Afghan immigrants as an angry, profane co-worker who used slurs and threatened violence.

Daniel Gilroy said Mateen started badgering him and sending dozens of text messages to him daily, and that he reported Mateen’s behavior to his bosses.

“I kind of feel a little guilty that I didn’t fight harder,” Gilroy said. “If I didn’t walk away and I fought, then maybe 50 people would still be alive today.”

Gilroy told multiple news outlets that Mateen routinely used slurs for gay people, blacks, Jews and women.

“He talked about killing people all the time,” Gilroy told The New York Times. Of the massacre, Gilroy said, “I saw it coming.”

In a statement, the company said Mateen was assigned to a residential community in South Florida. He had been subject to a “detailed company screening” when he was recruited in 2007 and was re-screened in 2013 “with no adverse findings,” the company said.

Mateen graduated from Indian River Community College in 2006, the same year he changed his name from Omar Mir Seddique to Omar Mir Seddique Mateen, according to civil court records in St. Lucie County. The papers listed no reason for the name change.

His ex-wife, Sitora Yusufiy, said her former husband wanted to be a police officer and had applied to the police academy. He eventually joined G4S, a global security firm that has 610,000 employees in about 100 countries.

Yusufiy told reporters in Boulder, Colorado, that she believed Mateen suffered from mental illness.

Although records show the couple didn’t divorce for two years after their 2009 marriage, Yusiufiy said she was actually with Mateen for only four months because he was abusive. She said he would not let her speak to her family and that family members had to come literally pull her out of his arms.

Divorce papers reveal that Mateen made $1,600 a month working for G4S and that she earned $3,000 a month as a real estate agent.

It’s unclear when Mateen married his second wife, Noor Salman, but an Aug. 30, 2013, property deed in Saint Lucie County identified them as a married couple.

Family members said the pair had a young son about 3 years old.

Mateen had no criminal record, but he was not unknown to law enforcement.

In 2013, he made inflammatory comments to co-workers, and he was interviewed twice, FBI agent Ronald Hopper said. He called those interviews inconclusive.

The following year, Hopper said, officials found that Mateen had ties to an American suicide bomber. He described the contact as minimal, saying it did not constitute a threat at the time.

After the attack, authorities immediately began investigating whether it was an act of terrorism.

Mateen appears to have been a “homegrown extremist” who espoused support for a jumble of often-conflicting Islamic radical groups, the White House and the FBI said Monday.

FBI Director James Comey said Mateen was clearly “radicalized,” at least in part via the internet.

Orlando Police Chief John Mina said the gunman made a 911 call from the nightclub professing allegiance to the Islamic State.

Mateen purchased at least two firearms legally within the last week or so, according to Trevor Velinor of the Bureau of Alcohol, Tobacco and Firearms.

Mateen attended evening prayer services at Port St. Lucie’s Islamic Center three to four times a week, most recently with his son, Rahman said. The imam said he last saw Mateen on Friday.

“When he finished prayer, he would just leave,” Rahman told The Associated Press. “He would not socialize with anybody. He would be quiet. He would be very peaceful.”

On Monday, the shooter’s father, Seddique Mir Mateen, said what his son did “was the act of a terrorist.”

“I apologize for what my son did. I am as sad and mad as you guys are,” he told reporters outside his home. He did not go into details about his son’s religious or political views, insisting he did not know.

Asked whether he missed his son, the father said: “I don’t miss anything about him. What he did was against humanity.”

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Weiss reported from Charlotte, North Carolina.