Reports have emerged that Orlando gunman Omar Mateen, who killed 49 people, had attended the LGBT nightclub before and had used gay dating apps.
Regular at Pulse nightclub Kevin West said Mateen had messaged him a year before the shooting sporadically, using the gay dating app Jack'd, reports the Orlando Sentinel and the LA Times.
Mr West said the two had never met in person before but he recognised the gunman as he crossed the street at about 1am on Sunday (local time) -- an hour before the shooting.
At least four other regular patrons at Pulse too said they recognised Mateen.
"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, who also uses the name Aries, told The Orlando Sentinel.
He said he had seen him at the club at least a dozen times.
"We didn't really talk to him a lot, but I remember him saying things about his dad at times," Mr Smith said.
When Mr West realised Mateen was the shooter he turned his phone over to the FBI.
Officials said Mateen appeared to have been radicalised by IS over the internet, but sympathised with groups that were violently opposed to each other, the LA Times reported.
A man who says he was a fellow student in Mateen's 2006 police academy class has added to the claims. He said Mateen had once asked him out on a date. At the time the classmate, who did not want to be named, was not openly gay and refused.
"He just wanted to fit in and no one liked him," he told WFTV 9 ABC.
"He was always socially awkward."
Mateen was reportedly sighted multiple times at Pulse over three years, but his father disputes this firmly.
"If he was gay, why would he do something like this?" said Seddique Mateen.