The first dispatch went out at 12:39 a.m., when 911 received calls that "somebody is shooting inside the auditorium" of a movie theater in Aurora.
"There is at least one person that's been shot," a dispatcher says on the tapes, "but they're saying there's hundreds of people just running around."
"All available units, please respond to the theater."
"Someone is still shooting inside theater number nine, per an employee," the dispatcher tells officers.
Three minutes later, at 12:42 a.m., officers arrive on the scene, and see the first of 71 victims shot by the gunman.
"We've got another person outside shot in the leg, a female," the officer says. "I've got people running out of the theater, they're shot."
The chaos was originating from theater 9, where the midnight showing of "The Dark Knight Rises" had begun just half an hour earlier. Officers attempted to get into the theater, but it was too smoky.
At 12:44 a.m.: "Somebody is spraying gas in here. Do we have gas masks available?"
Officers, still unable to get into the theater because of the smoke, demand more help, their voices growing more urgent with each call: "Get us some damn gas masks to theater 9, we can't get in it."
Two minutes later, officers are finally able to enter the theater, seeing for the first time the severity of the situation.
"We need rescue inside the auditorium, we have multiple victims."
"I've got seven down in theater 9, seven down."
"I've got a child victim. I need rescue at the back door of theater 9 now."
At the same time, as officers inside the theater worked to gauge the damage and to help the shooting victims, officers outside the theater were tracking the suspect. Several officers were already at the theater at the time of the shooting because of the large crowds expected for the opening of the movie.
At 12:45 a.m.: "I need a marked car behind the theater, Sable side. I've got a suspect in a gas mask."
Less than a minute later, officers move in on the suspect.
"The white car in the rear of the lot, is that a suspect?"
"Yes, we've got rifles, gas masks. I've got an open door going into the theater."
"OK, hold that position, hold your suspect."
Incoming police cars were used to set up a perimeter around the mall. While officers detained the suspect outside the theater, officers inside worked to save the victims. The tapes revealed their frustration that backup wasn't arriving quickly enough to help all the victims.
At 12:48 a.m.: "Send me Denver cars this way too, I need more help."
Two minutes later, "I've got one ambulance here. Where are my ambulances at?"
As ambulances arrived, they began setting up in a nearby parking lot. But there still wasn't enough help for all the victims, as officers begin turning their cop cars into ambulances.
At 12:54 a.m.: "Do I have permission to start taking some of these victims via car? I've got a whole bunch of people shot out here and no rescue."
"Yes, load them up and get them out of here."
Ten victims of the shooting died at the scene, two others in the hospital. Fifty-nine others were injured, making this the largest mass shooting ever in America with 71 total victims.
A suspect, identified as James Holmes, was detained at the scene. Officers are still working to get into his home, which authorities say is booby trapped and highly dangerous. Holmes, 24, was a Ph.D. candidate at the University of Colorado Medical School.
Bodies of the 10 victims killed at the scene remained in the theater until 3 p.m. in Aurora, when authorities began removing them.
Officials told ABC News that Holmes bought a ticket for the movie, left minutes into the screening through an emergency exit and returned dressed in a gas mask and bulletproof vest, opening fire on the audience.
The FBI said about 100 of its agents are assisting local authorities with the ongoing investigation.