NASHVILLE, Tennessee - Video released on Tuesday showed Nashville, Tennessee, police officers storming a private Christian grade school on Monday before confronting and fatally shooting an attacker who killed three nine-year-old students and three adult staff members.

The six minutes of harrowing footage, edited together from the body-worn cameras of two responding officers and released by the Metropolitan Nashville Police Department, showed officers clearing several first-floor classrooms before heading upstairs to the second floor as gunfire is heard.

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

Police have identified the shooter as Audrey Elizabeth Hale, a 28-year-old former student at the Covenant School. Investigators are examining what they called a “manifesto” that Hale left behind, hoping to learn what motivated the latest in a long string of US mass shootings.

Monday’s violence marked the 90th school shooting – defined as any incident in which a gun is discharged on school property – in the US this year, according to the K-12 School Shooting Database, a website founded by researcher David Riedman.

Last year saw 303 such incidents, the highest of any year in the database, which goes back to 1970.

During a previous press briefing, Metro Nashville police chief John Drake said Hale self-identified as transgender, although Mr Drake offered no further clarity. The police chief and other officials repeatedly referred to the suspect with female pronouns, though Hale used male pronouns on a LinkedIn page that listed recent jobs in graphic design and grocery delivery.

Mr Drake said Hale had a detailed, hand-drawn map of the school showing various entry points. Hale was armed with two assault-style weapons, one of them a rifle, as well as a 9mm pistol, authorities said.

The police chief told NBC the mani...