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The call came shortly after 2:35 a.m. on June 12, 2016.

"I want to let you know, I'm in Orlando, and I did the shooting."

It was 29-year-old Omar Mateen, flatly telling a 911 operator that he was responsible for a mass shooting that would turn out to be the worst in modern American history: 49 people were killed and 53 were injured.

In the chilling audio, which a judge ordered the city of Orlando to release Monday, the operator asks what his name is.

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

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The phone call was one of several that Circuit Judge Margaret Schreiber ordered the city to release after news organizations requested more than 600, according to the Associated Press.

Two-thirds of the calls have already been released, the AP reported, but city attorneys have fought to withhold more than 200, citing the extreme suffering depicted in them.

For Demetrice Naulings, who survived the massacre but lost her close friend Eddie Justice, hearing the audio released Monday was difficult enough.

“It’s like I’m swallowing a brick,” she told NBC News, adding that she regretted having Mateen's voice in her head. Finally listening to it didn't appear to help her resolve the questions that have been haunting her since June 12.

"Why now? Why that night? Why that place?" she said. "Those are the questions that I'm always going to ask."

In other audio released Monday, Mateen can he heard speaking with a police negotiator who is identified as Andy. In the calls, Mateen at times speaks sharply and methodically, repeatedly declining to answer Andy’s initial questions, for instance, and instead insisting that Andy “tell America to stop bombing Syria and Iraq.”

At one point Mateen falsely claims that there are bombs outside of the club.

"And I'm going to ignite it if they try to do anything stupid."

When Mateen invokes Tamerlan Tsarnaev, who he describes as “his homeboy” who “did his thing at the Boston Marathon,” he sounds petulant, saying: “Now it’s my turn, okay?”

In other sections of the audio — such as when Andy asks about a vest that Mateen says he’s wearing — Mateen vanishes from the call and Andy is left pleading with him to return to the phone.

“I need some help from you,” Andy says. “We need to get this resolved peacefully. And we need your help to do that.”

Andy dials Matten’s phone repeatedly, but he has little luck negotiating with him. When Mateen finally answers, and Andy tells him that they need to stay in "constant contact," Mateen quickly replies: "No, no, no, no, no, no, no."

Shortly after, the line goes dead.