A small grey truck prowling the parking lot of The Covenant School in the upscale Nashville suburb of Green Hills was the first indication that something awful would occur.
Audrey Hale, 28, armed with two assault rifles and a 9mm handgun, approached the premises after passing by children on swings.
Hale dashed through the closed double glass doors and cautiously walked over the fragments.
The former transgender student at the Presbyterian elementary school held one rifle and draped the other over his shoulder. The firearms were engraved with Hale's chosen moniker, "Aiden," and the word "Hell."
Hale wore camouflage pants, a black military body vest over a white T-shirt, and a backward red baseball cap. In CCTV footage, the tiny figure appeared to be a teenager.
While inside, Hale crouched and pointed a gun while moving commando-style past a photocopier and stalked the empty hallways, entering and exiting a room labelled "church office" at one point.
Before continuing, the shooter passed the front desk and a door labelled "Children's Ministry" and peered inside to check if anyone was present.
The victims, three nine-year-olds and three adults were shot at random even thoHale, having prepared precise school mapsce, they received the first report at 10:13 a.m., and Officer Rex Engelbert arrived minutes later in his SUV.
His body camera footage revealed the courageous response of the other officers involved.
As Officer Engelbert parked, his dispatcher informed him that the shooter was believed in the first-floor main lobby.
He responded, "I'm going to make an entry on the front side,"
He swiftly retrieved a rifle with a sight from the back of his boot, and as he approached the school, a woman who appeared to be a teacher appeared.
She cried, "The kids are all locked down," "But we have two kids that we don't know where they are..."
Officer Engelbert performed his duties with great composure. Without breaking stride, he readied his rifle and assured the woman: "OK, Yes, ma'am."
He seized the keys from a school administrator and began to unlock the door. The woman informed him that there were gunshots in Fellowship Hall and "upstairs are a bunch of kids."
The officer cried to his arriving comrades, "Give me three! I need three; let's go!"
As he raced in with two colleagues shouting "Metro Police," sirens blared. They entered a corridor packed with backpacks stored in their respective cubbies.
We have no idea where he is, "One of the officers yelled. They dashed farther inside the building, bursting first into a classroom labelled "Mrs Chance."
They rushed into the little bathroom, decorated with children's artwork and unoccupied, searching for the perpetrator.
The following room was identified with a placard that read "Hope" As they entered the building, Officer Engelbert yelled, "With me, with me,"
The officers understood that the shooter could hide in ambush each time they entered a room, but they never hesitated, shouting "Clear!" and "Next!" and rushing on.
Like a soldier engaged in urban warfare, Officer Engelbert peered around corners and doors. At one point, he passed a preschooler-created rainbow painting.
Then, over the loud alarms, he yelled: "Gunfire!" "It is located upstairs! It appears to be upstairs!"
Then, he rushed passed a second officer on the stairs who was only armed with a handgun and not a rifle. The other officer stood on the sidelines and yelled, "Go, go, go."
On reaching a landing, Engelbert sped up and began sprinting down a corridor towards the direction of the gunfire, passing penguin photographs on a wall.
Where the corridor led onto an atrium, he discovered many coworkers already firing firearms at the perpetrator.
One cried, "reloading", and the other stated, "We've got one down" Officer Engelbert was signalled through by an officer who yelled, "Push up!"
As Officer Engelbert rounded a corner, he spotted the shooter's head peeking from behind an armchair close to a wide window.
He was approximately 20 feet away when he took the shot, fired a rapid burst, and killed Hale.
Officer Michael Collazo, who had also hurried up the steps and sped toward the gunfire, was to his right.
On the stairs, he yelled to his coworkers, "Keep pushing, go, shots fired, shots fired, move!"
After Officer Engelbert struck the subject, Officer Collazo advanced and yelled: "Quit moving! Quit moving!"
He yelled to a second officer: "Observe left! Observe left!" The officer then demanded that the suspect remove his hand from the gun.
Officer Collazo, who was now only a few feet away from the shooter, fired four times at him. He could be seen moving the firearms away from the incapacitated Hale on his bodycam footage. Heavy breathing, he yelled: "Put the suspect down! Put the suspect down!"
The time was 10:27, fourteen minutes after the firing had begun. The shooter was subdued by Officer Engelbert six minutes after his arrival outside the school.
In contrast to prior school shootings in the United States, the police responded quickly.
Officers in Uvalde, Texas, waited inside Robb Elementary School for more than an hour while a gunman in a classroom continued an attack that killed 19 children and two adults.
Yet in 2018, a handful of cops who responded to the school shooting in Parkland, Florida, did not quickly pursue the suspect, according to an investigation by a state panel. Seventeen pupils and staff members died.
The Covenant School was established in 2001 and had approximately 200 students aged three to eleven.
Officer Engelbert has been in the force for four years, while Officer Collazo served for nine.
At the time of the incident, there were no police officers posted to the school because it is a religious institution.
Former Boston Police Commissioner Ed Davis stated that the two cops and their colleagues had shown "incredible courage" and "saved lives."
He said: "A remarkably daring and successful response from the cops. The difficulty of starting to clear a building lies in the fact that any room you enter may have a shooter.
"These officers demonstrated exceptional skills for room clearance and communication. Specific training and response we would expect from police reacting to an incident of this nature."
He added: "Officers Engelbert and Collazo's tactics and techniques were extraordinarily effective and saved lives. This could not have been completed any faster."