Natalie Hammond thought it might have been the sound of pipes banging when the furnace kicks in.
Other teachers figured a janitor had knocked over a toolbox, or perhaps a stack of metal folding chairs had slipped off a cart, or maybe it was just the clang of the risers being set up for choir practice.
As clusters of tiny students drew gingerbread men and sang songs and twisted into yoga poses inside the classrooms of Sandy Hook Elementary School 380 days ago, few could comprehend the true source of that terrible noise echoing down the long hallways.
But as the bursts of gunfire continued, and the horrific reality came into unmistakable focus, a day of unfathomable grief and violence also became a day of quiet valor, from the teacher who kept a gunshot wound to her foot a secret so as not to frighten her students, to the Newtown police officer who sprinted toward an ambulance, cradling a gravely wounded girl in his arms and whispering "Come on, sweetie. Come on, sweetie" despite the terrible odds against her.
Friday's release of hundreds of police reports spanning thousands of pages offers the clearest picture yet of a terrifying rampage that shook the nation's psyche, sparking difficult debates coast-to-coast over guns and mental health care and school security.
But the reports are also a gripping reminder that the Dec. 14, 2012, attack is a decidedly local and human story as well, with wrenching tales of horror and heroism inside the sprawling schoolhouse down Dickinson Drive.
It began with the first shots, as Adam Lanza blasted out the glass doors at the front of the school, startling Principal Dawn Hochsprung, school psychologist Mary Sherlach and others who had just settled in for a nearby meeting with a parent.
It is well known that both women ran toward the sound, and were the first to be fatally wounded in the school. But they weren't alone in racing toward danger. Lead teacher Natalie Hammond was 10 or 15 feet behind Hochsprung and Sherlach as all three sprinted out of the meeting. When Lanza leveled his rifle at the women and fired, Hammond was struck in the left hand and left thigh and fell to the hallway floor. She lay motionless and saw Lanza standing over her colleagues and then moving on toward the classrooms. She crawled back into the meeting room, then lay by the doorway, using her right hand to hold the door closed as she heard footsteps and the sound of Lanza swapping out the magazines on his Bushmaster rifle.
With a second round of shots, teachers and others in the school began to fathom the unfathomable, and the police files hold numerous reports of quick thinking and quick action by staff.
School custodian Rick Thorne dialed 911 on his cellphone, then ran down unsecured hallways, warning teachers. Some were already aware of the danger and instantly applied lockdown protocols — locking doors, closing blinds, shutting lights, papering windows. They huddled students into corners, hid them under tables and bookcases, or hustled them into closets and bathrooms.
Kaitlin Roig crammed so many first-graders into her small bathroom that at one point six kids were standing on the toilet seat as she tried to figure out how to fit everyone in. When police liberated her room, Newtown Lt. Christopher Vanghele told her she had saved the children's lives.
Teachers, terrified in their own right as shots rang out by the dozens, devised schemes to calm their students, softly reading stories and playing word games and singing songs as they nervously gauged the shooter's proximity by the louder and softer sound of the gunfire.
Meanwhile, state and local police sped toward the school with the first chaotic reports of a possible shooter. There has been criticism of the decision to delay entering the school amid confusion over the number of gunmen, but it is clear that the first officers to breach the building did so with the belief that one or more armed suspects might be in the school, and might be looking to ambush police.
Inside, they moved in teams of three and four, guns drawn, sweeping rooms in a search for victims and survivors, still unaware of the horror that lay beyond the doors of two of the classrooms. It was smoky, with the acrid smell of gunpowder, and near the shooting scenes, officers had to step over spent shells that littered the floors.
The officers relied on training for the tactical rules of dealing with an active shooter. But nothing prepared them for the scenes inside classrooms 8 and 10.
Newtown Officer William Chapman knew that at least two adults had been killed at the school, but as he went from room to room, he initially found only empty spaces or groups of students and staff, frightened but unharmed. He approached Victoria Soto's classroom, expecting to find more of the same.
Chapman saw the Glock pistol first, and then Lanza's body, laying where he had shot himself. Chapman stepped inside, quickly scanning the room for a possible second shooter.
And then, he wrote, "my heart broke."
"I walked around the room saying to myself, 'no, no, no,'" Chapman wrote in his report.
The heartache only grew as he moved to the next room, where Lauren Rousseau was working as a substitute teacher. Like Roig, Rousseau had tried to protect her children by hiding them in the bathroom.
Chapman wrote that it appeared the teachers — Rousseau and special education aide Rachel D'Avino — "were actively trying to protect the children at all costs." But they died trying. And the image of the children in the bathroom, Chapman wrote, "was the most horrific thing that I had ever seen."
Chapman then seized on the idea that there must be a survivor. "I remember thinking 'someone has to be alive, the shooter is down, it's time to get people out of here.'"
He returned to Soto's room, moving from child to child, checking for a pulse. He found one in a young girl, and shouted for officers to provide cover while he brought her out of the school.
"I began running across the parking lot towards Dickinson Drive with the girl in my arms praying that she would live and telling her that she was safe, that Jesus loved her, and that I was protecting her," Chapman wrote.
The loss of so many children in Rousseau's and Soto's classrooms tested the resilience of many officers.
One state trooper literally went weak in the knees at the sight of the children. "I stepped out of the room and someone grabbed me and asked me if I was all right," he wrote. "I said no."
State Police Sgt. Brent Aiken said numerous fellow troopers were in shock as they left the school. The troopers "were all speechless and had a look of disbelief on their faces," he wrote.
When State Police Sgt. William Cario approached the bathroom in Rousseau's room, he was "initially unable to comprehend what I was looking at," he wrote. Cario fixated on one boy, and struggled to process the reality of so many other fallen children.
"The face of that little boy is the only specific image I have in that room," he wrote.
Cario tried to establish a count of the victims in the two classrooms, "but my mind would not count beyond the low teens and I kept getting confused," he wrote.
But Cario still had work to do. He was aware Natalie Hammond had been shot, and he returned to the meeting room, swiftly bandaging her hand and leg. He remembers trying to conserve medical equipment, thinking there might be other survivors in need of treatment.
Although Cario didn't think it was safe to evacuate everyone in the room, he put Hammond in a wheeled desk chair and brought her outside. Police were keeping ambulances a safe distance away, so Cario placed Hammond in another trooper's car and instructed him to drive up to the ambulance staging area.
Hammond repeatedly told Cario "Thank you" and "God bless you."
Later in the day, Cario bumped into Matthew Cassavechia, director of emergency medical services at Danbury Hospital, who said medical personnel would have to be given access to the school to formally declare the victims dead. Cario led Cassavechia and two other senior paramedics toward the building.
"I tried to prepare them for what they were about to see. I told them of the number of victims and the nature of the wounds," Cario wrote. "I told Cassavechia, 'This will be the worst day of your life.'"
The newly released documents also include limited and often heavily redacted reports of interviews with children who survived the shooting in Soto's room. Some had run out shortly after Lanza entered, and others escaped while Lanza was swapping ammunition magazines. Some interviews were conducted within hours of the shooting, as police sought to resolve reports that there might have been a second shooter.
One boy said he heard loud bangs and then the door opened and a "bad man" entered the room and started shooting. He said the man was dressed in "army clothes" and was firing a bazooka — the same word several other boys selected to describe the weapon.
The boy said he saw his teacher get shot as well as two of his classmates. He said the shooter "shot at him multiple times but missed" and instead struck a stuffed animal he was holding. The boy said he dropped the stuffed animal and ran.
Teachers and police did their best to keep students calm. A teacher shot in the foot explained away the blood by telling students in her classroom that she had stepped in red paint. Later, when other students asked if she was OK, she replied, "I'm just fine. I only sprained my ankle."
Officers wrestled with the desire to get the children out of the school as quickly as possible, but feared the possible traumatic impact of seeing Hochsprung and Sherlach. So students were told to put their hands on the side of their heads to create blinders, or to close their eyes and place their hands on the shoulder of the student ahead of them.
"I told them we were going to play follow the leader and whoever kept their eyes closed would win," Trooper First Class Edward Benecchi wrote.
The reports also show cautious teachers refusing to unlock doors even after police said it was safe to leave. Roig, who packed her students into the bathroom, was among the most skeptical, refusing to emerge even after an officer slid his badge under the door.
Chapman was there when Roig opened the door.
"A little girl ran up to me with her arms out," Chapman wrote, "and I picked her up and hugged her and told her that she was safe."
Courant Staff Writer Dave Altimari contributed to this storyCopyright © 2015, CT Now