A sign of support is part of a makeshift vigil following the Pulse nightclub shootings in Orlando. (Carlo Allegri/Reuters)

The FBI on Monday released a partial transcript of the conversations Orlando gunman Omar Mateen had with hostage negotiators and police dispatchers, and their dialogue reinforces that the 29-year-old was at least partly inspired by the Islamic State and intent on inflicting stunning destruction.

The exchanges are just one more piece of a puzzle that investigators are working to solve, but they offer perhaps the most detailed look yet into what Mateen may have been thinking as he carried out his rampage, which left 49 victims dead and dozens of others wounded, at the Pulse nightclub a week ago.

Talking on the phone from a bathroom where he was holed up with hostages, Mateen said that a vehicle outside contained explosives and that he would “ignite it” if police tried to “do anything stupid,” according to the transcript. He told those on the other end of the phone that he “did the shootings” and he vaguely threatened more attacks.

“In the next few days,” Mateen said, “you’re going to see more of this type of action going on.”

Mateen also swore fealty to the leader of the Islamic State. Authorities ultimately did not find any explosives.

FBI agent Ron Hopper explained the decision not to release the audio of the Orlando victims' 911 calls June 20, saying it would be too painful for those affected by the massacre at Pulse nightclub. However, the agency did release a partial transcript of shooter Omar Mateen's 911 call. (Reuters)

The Justice Department did not release a full transcript of all of Mateen’s exchanges with law enforcement, nor did officials provide any audio. Initially, the department redacted references to the Islamic State and its leader, Abu Bakr al-Baghdadi. The decision to do that drew intense criticism from Republicans, some of whom alleged that the administration was trying to minimize the shooting’s connection to the Islamic State.

“Selectively editing this transcript is preposterous,” House Speaker Paul D. Ryan (R-Wis.) said in a statement. “We know the shooter was a radical Islamist extremist inspired by ISIS. We also know he intentionally targeted the LGBT community. The administration should release the full, unredacted transcript so the public is clear-eyed about who did this, and why.”

Florida Gov. Rick Scott (R) echoed that sentiment in an interview with Fox News, calling the limited release “another example of not focusing on the evil here.”

The FBI and the Justice Department later released details of one exchange that included explicit mention of the Islamic State. Officials said they did not do so initially out of sensitivity for the victims and because they did not “want to provide the killer or terrorist organizations with a publicity platform for hateful propaganda.”

“Unfortunately, the unreleased portions of the transcript that named the terrorist organizations and leaders have caused an unnecessary distraction from the hard work that the FBI and our law enforcement partners have been doing to investigate this heinous crime,” the Justice Department and the FBI said in a joint statement.

The investigation of what prompted Mateen to carry out the attack is a little more than a week old, and many questions remain unanswered. Investigators have not publicly disclosed, for example, how many clubgoers might have been wounded by police fire in the chaotic encounter, nor have they specified Mateen’s reasons for attacking the popular LGBT nightspot.

“What I can tell you is that while the killer made these murderous statements, he did so in a chilling, calm and deliberate manner,” said Ron Hopper, FBI assistant special agent in charge, at a news conference Monday.

Hopper said that the bureau’s investigation “may last months or even years” and that investigators had conducted more than 500 interviews and collected hundreds of pieces of evidence. He said agents think Mateen “was radicalized domestically,” rather than directed by any foreign terrorist group, although they are looking at “myriad” things to determine a precise motive.

The partial transcript, though, reveals more nuance about the encounter. The first call about multiple shots being fired at the club came at 2:02 a.m., and two minutes later, more police officers arrived. Officers from various agencies entered the club at 2:08 a.m., and at 2:18 a.m., the SWAT team was called out.

At 2:35 a.m., Mateen made his first 911 call from the bathroom.

“In the name of God the Merciful, the beneficial,” he said, in Arabic, according to the transcript.

“What?” the call taker responded.

“Praise be to God, and prayers as well as peace be upon the prophet of God. I let you know, I’m in Orlando and I did the shootings,” Mateen said.

“What’s your name?” the call taker asked.

“My name is I pledge of allegiance to Abu Bakr al-Baghdadi of the Islamic State,” Mateen said.

Law enforcement and other officials have said previously that Mateen pledged his allegiance to the Islamic State during one of his calls to police, and he posted messages on Facebook doing the same. FBI Director James B. Comey and President Obama have said he appeared to have been motivated at least in part by extremist propaganda online.

Investigators have also explored claims that Mateen had used a dating app to seek men and had been to Pulse before the shooting, and officials have said they are investigating the crime as one of terror and hate.

Attorney General Loretta E. Lynch told CNN on Sunday that Mateen “didn’t get into” his thoughts about gay people during the calls, and the partial transcript shows no such discussion. Hopper said that allegations about Mateen being gay were “still being vetted out” and that investigators had reached no conclusions.

The FBI said Monday that Mateen, in addition to his contact with 911 operators, had three calls with crisis negotiators — the first at 2:48 a.m. lasting nine minutes, the second at 3:03 a.m. lasting 16 minutes and the third at 3:24 a.m. lasting three minutes. In those calls, Mateen “identified himself as an Islamic soldier,” the FBI said, and told the negotiator “to tell America to stop bombing Syria and Iraq.” The FBI said Mateen claimed that was why he was “out here right now.”

Mateen also claimed there was “some vehicle outside that has some bombs,” and he threatened, “You people are gonna get it, and I’m gonna ignite it if they try to do anything stupid,” according to the FBI transcript. He also said he had a vest like the kind “used in France.”

The calls came after Mateen twice exchanged gunfire with police officers at Pulse and fled to a bathroom, authorities have said. Orlando police officials have said the gunfire stopped after he entered that bathroom, and negotiations began. All the while, they have said, officers worked to free hostages, including those hiding in dressing rooms.

Some of those trapped in the bathroom with Mateen have described his phone calls previously, and law enforcement officials have noted other contacts. Mateen exchanged text messages with his wife and had at least one phone call with an acquaintance, law enforcement officials have said. The details of that call and those exchanges, though, are unclear, and the FBI has not said precisely how many calls Mateen made or to whom.

Negotiations ultimately broke down with Mateen about 5 a.m., authorities said, and SWAT officers scrambled to break holes in the walls to the bathroom and free those held captive. The FBI said Monday that about 12 minutes after they started doing so, they received reports of shots being fired. Mateen eventually came out one of those holes, police have said, where SWAT officers killed him in a final gun battle.

His body — which was transported separately from Pulse and held in a different building than the remains of the victims — has been released from the Orange County Medical Examiner’s Office, authorities confirmed Monday.

Abigail Hauslohner and Arelis Hernandez contributed to this report.