THOUSANDS of people have turned out in Orlando to mourn 49 people killed inside a gay nightclub, as investigators examined possible motives for the man who committed the worst mass shooting in modern US history.
The White House and the FBI said 29-year-old Omar Mateen, an American-born Muslim, appears to be a "homegrown extremist" who had touted support not just for Islamic State (IS), but other radical groups that are its enemies.
FBI director James Comey said: "So far, we see no indication that this was a plot directed from outside the United States, and we see no indication that he was part of any kind of network."
He added that Mateen was clearly "radicalised", at least in part via the internet.
Despite Mateen's pledge of support to IS, other possible explanations have emerged for the shootings.
His ex-wife said he suffered from mental illness, while his Afghan-immigrant father suggested he may have acted out of anti-gay hatred, claiming his son got angry recently after he saw two men kiss.
Questions have also emerged over whether Mateen was conflicted about his own sexuality.
Jim Van Horn (71) said Mateen was a "regular" at the popular Pulse nightclub in Orlando, Florida, where he would later kill at least 49 people.
"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.
On Monday night, just about a mile from Pulse in central Orlando, thousands of people gathered for a vigil to support the victims and survivors, with the names of the dead read aloud.
The event was held on the lawn of Orlando's main performing arts venue, where mourners created a makeshift memorial of flowers, candles and notes for the victims.
Mr Comey said the FBI is trying to determine whether Mateen had recently scouted Disney World as a potential target.
He defended the bureau's handling of Mateen during two previous investigations into apparent terrorist sympathies. As for whether there was anything the FBI should have done differently, "so far, the honest answer is, I don't think so," Mr Comey said.
Wielding an AR-15 semi-automatic rifle and a handgun, Mateen opened fire at Pulse in the early hours of Sunday in a three-hour shooting rampage and hostage siege that ended with a Swat team killing him.
During the attack, he called 911 to profess allegiance to IS.
US president Barack Obama said there is no clear evidence so far that Mateen was directed by the group, calling the attack an apparent example of "homegrown extremism".
Mr Obama will travel to Orlando tomorrow to pay respect to the victims and stand in solidarity with the community, according to the White House.
It has emerged that Mateen was added to a terror watch list in 2013 when he was initially investigated that year following a tip-off from co-workers, but was taken off it soon after the matter was closed. People on that database are not automatically barred from buying guns. Mateen purchased his weapons in June, long after his removal from the list.
Five of the wounded are reportedly in grave condition, meaning the death toll could rise. A call has gone out for blood donations.
IS-controlled radio has hailed the attack, and called Mateen "one of the soldiers of the caliphate in America". But it gave no indication the group planned or knew of the attack beforehand.
Mateen's father, Seddique Mir Mateen, said the massacre was "the act of a terrorist".
"I apologise for what my son did. I am as sad and mad as you guys are," he said.
