The man who the police say killed 49 people at a gay nightclub in Orlando early Sunday morning had visited the club at least a dozen times before carrying out his attack, a witness told the Orlando Sentinel on Monday.

The shooter, identified as 29-year-old Omar Mateen, may have also used several different gay dating apps, according to reports from MSNBC and the Los Angeles Times.

And a former classmate of Mateen's told The Palm Beach Post he believed Mateen was gay and that Mateen once asked him out romantically.

Three additional witnesses confirmed that they had seen Mateen at the gay nightclub more than once before.

"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," one witness, Ty Smith, told the Sentinel.

"We didn't really talk to him a lot," he added. "But I remember him saying things about his dad at times. He told us he had a wife and child."

Chris Callen, who performs at Pulse under the name Kristina McLaughlin, told The Canadian Press and CNN's Anderson Cooper that Mateen had been going to the bar one or twice a month "for at least three years."

Smith later told The Canadian Press that Mateen said he "couldn't drink when he was at home — around his wife, or family. His father was really strict."

Smith and Callen say they stopped talking to Mateen when he pulled a knife on them after they made a religious comment.

"He said if he ever messed with him again, you know how it'll turn out," Callen said.

Reports of Mateen's flashes of anger and aggression align with what Mateen's ex-wife, Sitora Yusufiy, told CNN on Sunday night.

"In the beginning he was a normal being that cared about family, loved to joke, loved to have fun, but then a few months after we were married I saw his instability," she said. "I saw that he was bipolar and he would get mad out of nowhere. That's when I started worrying about my safety."

She told reporters earlier on Sunday that Mateen had beat her and emotionally abused her while they were married from 2009 to 2011.

'He was very creepy in his messages'

An Orlando man told MSNBC's Chris Hayes on Monday that he had seen photos of Mateen on the gay dating apps Grindr, Adam4Adam, and Jack'd over the past several years. At least two of the man's friends had been contacted by Mateen on the apps.

"He was very creepy in his messages, and I blocked him immediately," the man said.

Kevin West, another regular at Pulse nightclub, told the Los Angeles Times that he chatted with Mateen on and off for a year on the app Jack'd but had never met him in person. Incredibly, West said he met him for the first time as he was dropping a friend off at Pulse on Saturday night.

"He walked directly past me," West said. "I said, 'Hey,' and he turned and said, 'Hey,'" and nodded his head, West said. "I could tell by the eyes."

A regular performer at Pulse told Cooper of CNN that he saw Mateen there a couple of times a month, often with another man.

The reports come after Samuel King, a drag queen, told The Daily Beast that he had befriended Mateen while the two worked next door to each other in Fort Pierce. King said Mateen had seemed generally accepting of the fact that he and his friends were openly gay. King said he even recalled Mateen going at least once to the nightclub where King performed.

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'He was always socially awkward'

A former police academy classmate of Mateen's told The Palm Beach Post on Monday he thought Mateen was gay and that Mateen once asked him out romantically.

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