The Orlando shooter pledged allegiance to the leader of the Islamic State in a phone call to authorities during the attack, FBI phone transcripts released Monday show.
"I pledge allegiance to Abu Bakr al-Baghdadi ... on behalf of the Islamic State," Omar Mateen said in a transcript released without redactions by federal law authorities.
The transcript was initially released with both al-Baghdadi and Islamic State redacted. The decision to release parts of the transcript without redactions came after the US Justice Department was criticized for the move, namely by Republican Speaker of the House Paul Ryan who called it "preposterous."
"We know the shooter was a radical Islamist extremist inspired by [Islamic State]," Ryan said in a statement. "The administration should release the full, unredacted transcript so the public is clear-eyed about who did this and why."
Explaining its later decision to provide an unredacted transcript, the FBI said that furore was causing an "unnecessary distraction" from the FBI's work and that it was committed to "the highest level of transparency possible under the circumstances.”
In the transcript, Mateen made threats about car bombs and suicide vests in calls with authorities during the June 12 attack in which 49 people were killed and another 53 were injured in a gay nightclub. Mateen was shot dead by police and no bombs or vests were found.
According to the written phone transcripts, shots were first reported at the Pulse nightclub at 2:02 am. At 2:08 am police first engaged the suspect inside the club.
Mateen called the 911 emergency operator at 2:35 am and claimed responsibility for the shootings. The conversation, in which the suspect spoke partly in Arabic, lasted 50 seconds before he hung up.
The second call was with police crisis negotiators at 2:48 am and lasted nine minutes. A third call at 3:03 am lasted 16 minutes, and a fourth at 3:24 am extended three minutes.
According to the FBI, the shooter identified himself as "an Islamic soldier," and demanded that the US stop bombing Syria and Iraq, which he said was the reason he was "out here right now."
The United States leads a coalition trying to destroy the radical Islamic State group, which has declared parts of Syria and Iraq its caliphate.
The assailant said that if the police tried anything "stupid," he would set off car bombs. He also said he was wearing a suicide vest similar to the ones used in the November Paris attacks.
"In the next few days, you're going to see more of this type of action going on," Mateen told police, according to the transcript.
At 4:21 am, police removed an air conditioning unit from one of the club's dressing rooms in order to evacuate hostages. Those rescued told police at 4:29 am that the assailant said he was going to outfit hostages with suicide belts. It was this information that pushed police to move on the shooter, Orlando police chief John Mina said.
At 5:02 am, authorities used an explosive to blow a hole in the club wall so an armoured vehicle could gain access. As more hostages were rescued, police exchanged gunfire with Mateen and killed him at 5:15 am.
The FBI document did not provide any insight into whether the assailant single-handedly killed all 49 victims, or if some may have been hit by police in the rescue action.
Speaking to media Monday, Mina rejected the suggestion that the police waited too long to act during the attack. Authorites spent the time negotiating with the shooter and rescued hostages in the process, he said.