Most of the people who knew Omar Mateen are surprised he targeted the nightclub where he killed 49 people and wounded of 53 more.
One patron of the Pulse nightclub told The Orlando Sentinel he saw Mateen drinking at the bar at least a dozen times before the shooting.
"Sometimes he would go over in the corner and sit and drink by himself, and other times he would get so drunk he was loud and belligerent," Ty Smith said.
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.
He said the Orlando attack "was totally unexpected."
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But one colleague at the security contractor G4S, his most recent employer, 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 behaviour 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, Mateen's employer G4S said he had been subject to a detailed screening when he was recruited in 2007 and was re-screened in 2013 "with no adverse findings."
On Monday, the shooter's father, Seddique Mir Mateen, said what his son did "was the act of a terrorist."
"I apologise 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."
