Omar Mateen, 29, a U.S. citizen of Afghan descent who was working as a security guard, likely was "self-radicalised.
The gunman who killed 49 people at a gay nightclub in Florida threatened to detonate a car rigged with bombs and to strap hostages into explosive vests, according to partial transcripts of his 911 calls released on Monday.
The FBI published the heavily redacted text of Omar Mateen's conversations with a dispatcher and crisis negotiators and sought to fend off criticism that police may have acted too slowly to end a three-hour standoff on June 12 at the Pulse nightclub in Orlando, the worst mass shooting in modern U.S. history.
"You people are gonna get it, and I'm gonna ignite it if they try to do anything stupid," Mateen said during one of the calls, according to the FBI transcript.
"While the killer made these murderous statements, he did so in a chilling, calm and deliberate manner," FBI Assistant Special Agent in Charge Ron Hopper told a news conference.
Mateen also said he was wearing an explosive vest like the kind "used in France," apparently referring to the deadly assault in Paris last November by Islamic militants, the transcript said.
As patrons fled Pulse, they told police outside that the shooter said he was going to put four vests with bombs on victims within 15 minutes, the FBI said.
No explosive vests or bombs were found in the club or the suspect's car, however, the FBI said.
Mateen, 29, a U.S. citizen of Afghan descent who was working as a security guard, likely was "self-radicalised," federal agents have said.
He referred to himself as an "Islamic soldier" in one call, according to the transcript, and told a negotiator to tell the United States to stop bombing Syria and Iraq.
The transcript did not include a pledge of loyalty that authorities say Mateen made to the leader of the Islamic State militant group. Hopper said that only a partial transcript was released so as not to "propagate violent rhetoric."
'This Is Evil'U.S. House of Representatives Speaker Paul Ryan called for the full text to be released and accused the Obama administration of censoring references to Islamic State. He said the decision to edit the transcript was "preposterous" and that everyone knew Mateen was a radical Islamic extremist inspired by Islamic State.
"We also know he intentionally targeted the LGBT community," the top elected Republican official said. "The administration should release the full, unredacted transcript so the public is clear-eyed about who did this and why."
Florida's Republican governor, Rick Scott, agreed and questioned why the text was redacted.
"It doesn't make any sense to me," Scott said during an interview on FOX News Channel's "America's Newsroom." "This is evil ... It's clearly a result of evil, radical Islam. We've got to call this what it is. We've got to defend our country."
The White House said the decision on what to redact was made the Justice Department.
The attack renewed debate about gun control in the United States.
The U.S. Senate was set to vote on Monday on four competing measures - two from Democrats and two from Republicans - to expand background checks on gun buyers and curb gun sales for people on terrorism watch lists.
None of the bills was expected to achieve the 60 votes needed for passage in the 100-seat chamber, as Republicans and Democrats have not been able to reach consensus.
Investigators have conducted more than 500 interviews about the massacre, which also left 53 people wounded, Hopper said, and have processed more than 600 pieces of evidence.
Authorities have said that preliminary evidence indicates Mateen was a mentally disturbed individual who acted alone and without direction from outside networks.
Orlando Police Chief John Mina said the initial engagement by authorities caused the gunman to retreat and barricade himself in a bathroom with hostages, and that officers were inside the club saving victims during the standoff.
"I am very confident that they saved many, many, many lives that night," Mina said, rejecting any criticism that police had failed to act quickly enough to end the siege.
"Those killings are on the suspect and on the suspect alone," Mina told the news conference. "It was a very difficult decision but it was the right decision and I stand by it."
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