The gunman who killed 49 people at a gay nightclub appears to have been a "homegrown extremist", the White House and the FBI 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," said FBI Director James Comey. But he said Omar Mateen was clearly "radicalised," 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.
Despite Mateen's pledge of loyalty 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 said his son got angry recently about seeing two men kiss.
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."
More details of the bloodbath emerged, with Orlando Police Chief John Mina saying Mateen was "cool and calm" during phone calls with police negotiators.
But the chief said he decided to send the SWAT team in and bash through a wall after Mateen holed up with hostages in a bathroom and began to talk 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.
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Five of the wounded were reported in grave condition, meaning the death toll could rise. A call went 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 ISIS 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-Qaeda and to be a member of Hezbollah, too, Comey said.
He was also quoted as saying he hoped that law enforcement would raid his apartment and assault his wife and child so that he could martyr himself.
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.
