Patrons of Pulse Orlando, where Mateen opened fire on revellers, kiling 49 people and wounding scores more, said they had previously seen him at the club – while others claimed they had chatted to him on apps and websites such as Grindr.
The claims have raised questions over whether Mateen, who was married with a wife and child, was conflicted about his own sexuality, despite his family claiming the massacre could have been motivated by homophobia after seeing two men kiss while on a recent visit to Miami.
Meanwhile, FBI Director James Comey said that Mateen was clearly “radicalised”, at least in part via the internet, but said there was “no indication” that he was part of any kind of wider terrorist network, despite Mateen having phoned 911 during the attack to profess allegiance to IS.
He added that the FBI is trying to determine whether Mateen had recently scouted Disney World as a potential target.
Jim Van Horn, 71, said Mateen was a “regular” at the club. “He was trying to pick up people. Men,” Mr Van Horn said.
Mr Van Horn acknowledged that he did not know Mateen well, but said he suspects that the massacre was less about Islamic extremism and more about a man conflicted about his sexuality.
Ty Smith and Chris Callen, a couple who perform as drag-dancing performers at Pulse, said they had seen Mateen more than a dozen times at the club.
“I’ve seen him a couple of times at Pulse, a couple of other people that I’ve spoken with, including an ex-security guard, have actually witnessed this guy at Pulse many times before,” said Callen, who performs as Kristina McLauglin.
A former classmate of Mateen from his 2006 police academy class, said Mateen had asked him out and said he had visited gay bars with him.
Meanwhile, Mateen’s father, Seddique Mateen, denied his son was gay.“It’s not true. Why, if he is gay, would he do this?” he said.