As clubgoers ran for their lives to various corners of the building, calls came in from restrooms, the kitchen, an office:
"[Caller] is shot in the leg and knee."
"People in bathroom are also shot."
"[Caller advises} his friend has been shot in the chest."
[Caller advises] victim is losing a lot of blood."
Within a half-hour, details about the shooter began to trickle in.
"Subj has chinstrap facial hair," a dispatcher noted at 2:25 a.m.
At 2:34 a.m., another typed in, "long gun shell casings."
Six minutes later, the log shows that the shooter was "saying he pledges to the Islamic State," followed by "shooter saying possible explosives in the parking lot."
At 2:51 a.m., a victim told police the shooter had several bombs strapped to him, which turned out not to be true.
"Subj advises that he is a terrorist," the next log notation said.
Clubgoers trapped inside continued to call to report on their whereabouts, the condition of the injured and Mateen's movements:
"Small dressing room [possibly] hears reloading."
"I subj trying to leave small dressing room... staying put now ... hearing screaming."
"Vic is ... losing a lot of blood from leg and ribs."
At 4:21 a.m., the grim notes are interrupted by a glimmer of good news: "People are evacuating out of dressing room window through AC."
Then, at 5:02 a.m., the notes begin describing the police operation to enter the club.
"SWAT breached," the log said at about the time officers used explosives and an armored vehicle to break through a wall.
"[Caller] heard 4 explosions, desk heads them in [background], it continued.
"Shots fired north bathroom," was the update at 5:14 a.m.
Less than a minute later, dispatchers noted Mateen was down. And two minutes later, further confirmation that the worst mass shooting in modern U.S. history was over.
"Bad guy down strapped," the log said.
Tracy Connor is a senior writer for NBC News. She started this role in December, 2012. Connor is responsible for reporting and writing breaking news, features and enterprise stories for NBCNews.com. Connor joined NBC News from the New York Daily News, where she was a senior writer covering a broad range of news and supervising the health and immigration beats. Prior to that she was an assistant city editor who oversaw breaking news and the courts and entertainment beats.
Earlier, Connor was a staff writer at the New York Post, United Press International and Brooklyn Paper Publications.
Connor has won numerous awards from journalism organizations including the Deadline Club and the New York Press Club.
She lives in Brooklyn, N.Y.
Tom Winter is a New York-based correspondent covering crime, courts, terrorism and financial fraud on the East Coast for the NBC News Investigative Unit.