The six minutes of footage, edited together from the body-worn cameras of two responding officers and released by the Metropolitan Nashville Police Department, showed police armed with rifles storming into the building and conducting a room-by-room search.

WATCH VIDEO

After clearing several first-floor classrooms, the officers run upstairs to the second floor as gunfire is heard.

The officers run down a hallway – past what appears to be a prone victim – and into a lounge area, where the suspect is seen dropping to the floor after being shot.

Investigators were examining a “manifesto” written by Audrey Elizabeth Hale, the 28-year-old former student at the Covenant School identified as the attacker, hoping to learn what motivated the latest US mass shooting.

Hale was under a doctor’s care for an “emotional disorder” and had purchased seven guns ahead of the shooting, the city’s police chief said on Tuesday.

Hale employed two assault weapons and a handgun during the assault on the primary school, the latest in a long string of US mass shootings that have turned guns into a hot-button political issue.

Those three guns were among seven Hale bought legally from five area stores, Metropolitan Nashville Police Chief John Drake told reporters on Tuesday.

Hale’s parents did not know that Hale was in possession of seven guns, the chief said, adding that they were under the impression that the suspect had owned only one gun but had sold it.

Drake said it appeared that the suspect had some sort of training with firearms.

Hale fired on officers from the second floor as they arrived in patrol cars while standing back from large windows to avoid becoming an easy target.

Drake said Hale self-identified as being transgender although Drake offered no further clarity.

Drake and other officials repeatedly referred to the suspect with female pronouns.

Hale used male pronouns on a LinkedIn page that listed recent jobs in graphic design and grocery delivery.

Among various pieces of evidence under examination by police and FBI agents conducting an investigation were some writings by the assailant, including the manifesto and a detailed hand-drawn map of the school showing various entry points, Drake said.

Drake told NBC the manifesto “indicates there was going to be shootings at multiple locations and that the school was one of them”.

Investigators believe Hale harboured “some resentment for having to go to that school” as a child, he said without elaborating.

Police began receiving calls about a shooter at 10.13am, police spokesman Don Aaron told reporters.

The suspect was pronounced dead by 10.27am.

“The police department response was swift,” Aaron said.

The body camera footage showed officers rapidly searching for the shooter, in contrast to the videos showing officers in Uvalde, Texas, waiting inside Robb Elementary School for more than an hour as a shooter continued his attack inside a classroom on May 24.

That incident, where 19 children and two adults where killed, called into question the urgency with which police officers respond to mass shootings.

The start of the Nashville police video shows an officer retrieving a rifle from his trunk before a staff member directs him to the entrance, telling him that the school is locked down but at least two children are not accounted for.

“Let’s go! I need three!” the officer yells as he uses a key to unlock a door and enter the building, where alarms can be heard ringing.

When the officers reach the second floor, one says, “We’ve got one down,” before they race down the hallway to confront the shooter.

Officer Rex Engelbert and Officer Michael Collazo – whose body cameras provided the footage – both fire several rounds at the suspect.

The video shows the assailant still moving on the ground as another officer repeatedly yells, “Get your hands away from the gun!”.