The gunman whose attack on a nightclub left 49 victims dead appears to have been a "homegrown extremist" who espoused support for a jumble of often-conflicting Islamic radical groups, the White House and the FBI said Monday.

As Orlando mourned its dead with flowers, candles and vigils, counterterrorism investigators dug into the background of 29-year-old Omar Mateen, the American-born Muslim who carried out the deadliest mass shooting in modern U.S. history.

"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," said FBI Director James Comey. But he said Mateen was clearly "radicalized," at least in part via the internet.

Comey said the bureau is also 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.

The FBI chief defended the bureau's handling of Mateen during two previous investigations into his 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.

Despite Mateen's pledge of fealty to the Islamic State, a murky combination of other possible motives and explanations emerged, with his ex-wife saying he suffered from mental illness and his Afghan-immigrant father suggesting he may have acted out of anti-gay hatred. He said his son got angry recently about seeing two men kiss.

At least four regular customers at the Orlando nightclub said Monday that they had seen Mateen there before, the Orlando Sentinel reported.

"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 said.

Kevin West, a regular at the nightclub, said Mateen messaged him on and off for a year before the shooting.

Wielding an AR-15 semi-automatic rifle and a handgun, Mateen opened fire...read more at The Chicago Tribune