Omar Mateen used gay dating app Jack'd: witness

The gunman who shot 49 people dead at an Orlando gay nightclub used a gay dating app for a year before the massacre, a witness has claimed.

Kevin West, a regular at Pulse nightclub, said Omar Mateen messaged him on and off for 12 months using the gay dating app Jack'd, Los Angeles Times reports.

They had never met until an hour before Mateen opened fire on the packed club early on Sunday morning.

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

Mr West has turned his phone and Jack’d login information to the FBI for analysis.

Another Florida man, who asked not to be identified, said he thought Mateen was gay when they attended police academy together in 2006.

"We went to a few gay bars with him, and I was not out at the time, so I declined his offer," the former classmate told Palm Beach Post.

"He just wanted to fit in and no one liked him. He was always socially awkward."

Mateen’s father Sidiqque has emphatically denied his son was closeted.

"If he was gay, why would he do something like this?" Mr Mateen told Palm Beach Post.

In another interview, he said he still thinks of his son as "a good boy".

"In this month of Ramadan, the gay and lesbian issue is something that God will punish … (but) the servants of God shouldn't have anything to do with it,” he told LA Times.

Ty Smith and Chris Callen, a couple who performed drag shows at Pulse, said they had seen Mateen escorted drunk from the nightclub as many as a dozen times, beginning in 2013.

The pair told The Canadian Press they rejected the statement by the gunman’s father that his son was "disgusted" by seeing men kiss.

"That’s bullcrap, right there. No offence, that’s straight-up crap. He’s been around us," Mr Smith said.

"Some of those people did a little more than kiss outside the bar. He was partying with the people who supposedly drove him to do this?

"He’d get really, really drunk…he couldn’t drink when he was at home – around his wife, or family. His father was really strict, he used to bitch about it."

The pair said they had been disturbed when Mateen had reacted aggressively to a joke one of their friends had made.

"He ended up pulling a knife," Mr Callen said.

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

The FBI have said they believe Mateen was "radicalised" online.

The Pulse massacre is the worst mass shooting in US history, with 49 people confirmed dead and 53 in hospital.