Her voice quivers with each spoken syllable.
She's short of breath and high on adrenaline.
"I think there's somebody shooting in here, Sandy Hook School," Halstead, hiding beneath a desk in the school's infirmary, tells an unidentified emergency dispatcher by phone on the morning of Dec. 14, 2012.
"What makes you think that?" the voice on the other end of phone replies matter-of-factly.
"Because somebody's got a gun. I got a glimpse of somebody and they're running down the hallway. They're still running. They're still shooting. Sandy Hook School, please. Oh...."
And with the 24-second eyewitness account from Halstead, a school secretary who cheats death, the floodgates open for a deluge of 911 calls reporting the worst grade-school shooting in U.S. history.
Newtown officials relented Wednesday in their year-long campaign to block the public's access to the tapes, a week after a state Superior Court judge ordered their release.
For the first time, the real-time sounds of fear, bewilderment and confusion help convey the unspeakable toll of Lanza's shooting spree -- 26 lives lost in 11 minutes, 20 of them children, none older than 7.
The noise that really speaks volumes on the agonizing soundtrack doesn't belong to a human, however.
The blast of an assault rifle can be heard nine times in the background, maybe ten, but that last shot could be the final self-inflicted gunshot from a semi-automatic Glock handgun by the mentally-disturbed Lanza.
"It's still happening. I keep hearing shooting. I keep hearing popping," Rick Thorne, the school's acting head custodian and the next person to call 911, reports to an emergency dispatcher.
Thorne is standing in an empty hallway of the school, which is under a lockdown. There's a sense of urgency in his voice, but he's relatively composed.
"There's...I believe there's shooting at the front -- at the front glass. Something's going on," Thorne advises.
Thorne gives the dispatcher a lay of the land, from the address of the school to the potential location of the shooter in the building. Another two minutes will pass before the first Newtown police officer arrives at the scene, according to chronology prepared by investigators.
"All right, I want you to take cover," the dispatcher instructs Thorne before giving a directive to a female dispatcher. "Jen, get the sergeant. All right, get everybody you can going down there."
Thorne's instinct is to help when the dispatcher asks him if he can see anything out the window, however.
"No. It's still going on. I can't get over there," he says.
Words of caution follow from the dispatcher.
"OK, I don't want you to go over there. I want to know what's happening with the students, though, along the front corridor."
The plainspoken Thorne is caught somewhat off guard in his next exchange with the dispatcher, who says, "So at this time you're defending in place."
"Excuse me?" Thorne responds.
The nightmare is still unfolding near the front of the school, where first graders have resorted to hiding in a bathroom and Halstead is holed up in a first-aid supply closet. Keenly aware that their pupils are looking to them for protection and reassurance, teachers are trying to project calm in the face of evil.
"The door's not locked yet. I have to go lock the door," an unidentified female teacher confides to a dispatcher on an ensuing 911 call from inside her classroom near the school's entrance.
In this case, the teacher is the pupil.
"Keep everybody calm. Keep everybody down. Get everybody away from the windows, OK?" the dispatcher directs her.
The worst may be over.
"Now it's silent," Thorne updates the dispatcher.
But the sound of silence is deceiving.
"There's still shooting going on, please," Thorne declares.
Newtown reaches the point of no return.
"Jen, I need you to call the state police," one dispatcher is heard telling another, the directive punctuated by another gunshot.
"There's still...it's still going on," an exasperated Thorne says.
Newtown officials released seven audio files in total Wednesday through a Danbury law firm that acts as the town's corporation counsel. One of the files was a duplicate, so there are actually six audio files. They do not include additional 911 calls fielded independently by state police, who have not furnished the public with those recordings.
An unidentified woman overcomes not only psychological trauma but a gunshot wound to her foot to dial 911. She's in a classroom full of children facing the playground. There are two other adults taking cover behind a bookshelf in the room.
"Are you safe right now?" the dispatcher asks.
"I think so. My classroom door is not locked," the caller, surprisingly calm for a person in her condition, answers.
"Is there anyone who can lock the classroom without...with being safe," the dispatcher asks.
"No. There are children in this room, too."
The dispatcher relays first aid tips to the caller and lets her know that help is on the way.
"Try to keep pressure on it. Okay? We have people coming. Are you okay right now?"
"For now," the teacher signs off with a pause, "hopefully."
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