The man behind the worst mass shooting in recent US history visited the gay nightclub where he carried out the massacre several times, witnesses say.
Chris Callen, a performer at Pulse in Orlando, Florida, told the Daily News that Omar Mateen had been attending the venue for the past three years.
Investigators have not yet commented on the reports.
Mateen opened fire in the packed club early on Sunday, leaving 49 people dead and dozens wounded.
“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 Chris Callen.
In one incident, Mr Callen said Mateen pulled a knife on a friend after being angered by a religious joke.
Despite this, Mr Callen said Mateen was a “nice guy… Maybe he got radicalised and hated who he was.”
“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 told the Orlando Sentinel.
And another man, Kevin West, told the Washington Post he saw Mateen walking into Pulse in the early hours of Sunday, having already met him through dating app Jack’d.
“I remember details,” said Mr West. “I never forget a face.”
Mateen pledged allegiance to so-called Islamic State (IS) shortly before the attack, US authorities say.
FBI Director James Comey said there were “strong indications of radicalisation and of potential inspiration by foreign terrorist organisations”.
President Obama said the inquiry was being treated as a terrorist investigation, but added there was no clear evidence that Omar Mateen was directed by IS.
He will travel to Orlando on Thursday to pay his respects to the victims.
The two likely main challengers to replace him as US leader, Republican Donald Trump and Democrat Hillary Clinton have offered differing views on how to prevent such attacks recurring.
Mr Trump proposed suspending immigration from countries with links to militant attacks targeting the US or its allies.
But Mrs Clinton warned against “anti-Muslim rhetoric”, calling for better background checks on weapons sales.
Vigils have meanwhile been held in Orlando and around the world for the victims of the attacks.
Thousands of people gathered in central Orlando on Monday night, holding candles and flowers in tribute.
Imam Muhammad Musri, of the Islamic Society of Central Florida, said the attack had been “an act of terror, an act of hate”.
“We condemn the ideology of hate and death and destruction and we call for all Muslim leaders and communities across this nation and across the world to stand up and to deal with this cancer and to remove it once and for all,” he said.