ORLANDO, Fla. (AP) -- As thousands in Orlando turned out to mourn 49 people killed inside a gay nightclub, federal investigators examined possible motives for the gunman who committed the worst mass shooting in modern U.S. 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 the Islamic State, but other radical groups that are its enemies.
"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," FBI Director James Comey said Monday. He said Mateen was clearly "radicalized," at least in part via the internet.
Despite Mateen's pledge of support to the Islamic State, other possible explanations emerged. His ex-wife said he suffered from mental illness. His Afghan-immigrant father suggested he may have acted out of anti-gay hatred, and said his son got angry recently about seeing two men kiss. But questions 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 where he'd later take hostages and leave 49 dead.
"He was trying to pick up people. Men," Van Horn told The Associated Press late Monday outside the Parliament House, another gay club.
Van Horn, a retired pharmacist, said he met Mateen once, and the younger man talked about his ex-wife. But Van Horn said his friends soon "told me they didn't want me talking to him, because they thought he was a strange person."
Van Horn acknowledged that he didn't know Mateen well, but said he suspects that the massacre was less about Islamic extremism and more about a man conflicted about his sexuality.
"I think it's possible that he was trying to deal with his inner demons, of trying to get rid of his anger of homosexuality," said Van Horn, who lost three friends in the shooting. "It's really confusing to me. Because you can't change who you are. But if you pretend that you're different, then you may shoot up a gay bar."
The Orlando Sentinel and other news organizations quoted other regulars from Pulse who said they had seen Mateen there a number of times.
"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," said Ty Smith, who remembered seeing Mateen inside at least a dozen times.
On Monday night, just about a mile from Pulse in downtown Orlando, thousands gathered for a vigil to support the victims and survivors. The names of the dead were read aloud. It 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.
Many said they felt compelled to attend because of the role Pulse played in their lives.
People hold candels and lights during a vigil in solidarity outside Manhattan's historic Stonewall Inn to express their support for the victims killed at Pulse nightclub in Orlando in New York on June 13, 2016.
(Photo credit: KENA BETANCUR/AFP/Getty Images)
"It was a place that a young 20-year-old who wasn't openly gay felt safe for the first time," said Cathleen Daus, now 36, who worked at Pulse in her 20s. "Pulse gave me confidence, made me realize I was normal and so much like everyone else."
Some, including Jason Primar, who lost two friends in the massacre, released balloons that flew high above the downtown skyscrapers.
Primar went to Pulse at 2 a.m. Sunday, hoping for a good time with friends. Instead, he was greeted with gunshots and worries about those inside.
"I felt like I was over in Iraq," he said. He called his two friends inside; they never answered. He later discovered they died.
Comey said the FBI also was trying to determine whether Mateen had recently scouted Disney World as a potential target, as reported by People.com, which cited an unidentified federal law enforcement source.
"We're still working through that," Comey said.
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," Comey said.
Wielding a semi-automatic rifle and a handgun, Mateen opened fire at Pulse early 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 the Islamic State group.
ORLANDO, FL - JUNE 12: FBI agents investigate near the damaged rear wall of the Pulse Nightclub where Omar Mateen allegedly killed at least 50 people on June 12, 2016 in Orlando, Florida. The mass shooting killed at least 50 people and injuring 53 others in what is the deadliest mass shooting in the country's history. (Photo by Joe Raedle/Getty Images)
At the White House, 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." Obama will traveling to Orlando on Thursday to pay respect to the victims and stand in solidarity with the community, according to the White House.
More details of the massacre emerged, with Orlando police Chief John Mina saying Mateen was "cool and calm" during phone calls with negotiators. But Mina said he decided to send the SWAT team in and bash through a wall after Mateen holed up with hostages in a bathroom and talked about bombs and an explosive vest.
"We knew there would be an imminent loss of life," Mina said. As it turned out, Mateen had no explosives with him.
The tragedy hit the city's gay and Hispanic communities especially hard. Sunday was Latino Night at the club.
"As the names come out, they are overwhelmingly Latino and Hispanic names," said Christina Hernandez, a Hispanic activist. "These were not just victims of the LBGT community, but of the Hispanic community, as well. This was senseless bloodshed."
Five of the wounded were reported in grave condition, meaning the death toll could rise. A call has gone out for blood donations.
Mateen's grasp of the differences between Islamic extremist groups appeared shaky.
During three calls with 911 dispatchers, Mateen not only professed allegiance to the Islamic State but also expressed solidarity with a suicide bomber from the Syrian rebel group Nusra Front, and a few years ago he claimed connections to Hezbollah, too - both ISIS enemies, according to Comey.
The FBI became aware of Mateen in 2013 when co-workers reported that the private security guard claimed to have family connections to al-Qaida and to be a member of Hezbollah, too, Comey said. He was also quoted as saying he hoped law enforcement would raid his apartment and assault his wife and child so that he could martyr himself.
The FBI launched a 10-month preliminary investigation, following Mateen, reviewing his communications and questioning him, the FBI chief said. Mateen claimed he made the remarks in anger because co-workers were teasing him and discriminating against him as a Muslim, and the FBI eventually closed the case, Comey said.
His name surfaced again as part of another investigation into the Nusra Front bomber. The FBI found Mateen and the man had attended the same mosque and knew each other casually, but the investigation turned up "no ties of any consequence," Comey said.
Mateen was added to a terror watch list in 2013 when he was investigated, but was taken off it soon after the matter was closed, according to Comey.
People who are in that database are not automatically barred from buying guns. Mateen purchased his weapons in June, long after his removal from the list.
The Islamic State's radio 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.
Counterterrorism experts have been warning in the past few years about the danger of so-called lone wolf attackers who act in sympathy with extremist groups but aren't directed by them.
Mateen's father, Seddique Mir Mateen, said the massacre was "the act of a terrorist," and added: "I apologize for what my son did. I am as sad and mad as you guys are."
He wouldn't go into details about his son's religious or political views, saying he didn't know. Asked whether he missed his son, he said: "I don't miss anything about him. What he did was against humanity."
Associated Press writers Eric Tucker in Washington; Allen Breed, Mike Schneider and Tamara Lush in Orlando; and photographers Chris O'Meara in Orlando and Alan Diaz in Fort Pierce contributed to this report.