We now know the attacker was a 28-year-old who identified as a transgender male (a biological woman), by the name of Audrey Elizabeth Hale - initially police thought they were a teenager.

They were a former student at the school and a Nashville resident who lived with their parents.

Hale, who had no criminal history, was armed with two "assault-style" rifles and a pistol, and officers received reports of the attack at 10.13am (4.13pm UK time).

The killer had entered the building by shooting through glass doors before carrying out the attacks.

In a video released by police, Hale wore a black vest over a white T-shirt, camouflage trousers and a backwards red baseball cap as they roamed the school premises with the rifle brandished.

In response to the shootings, two officers opened fire and fatally shot Hale at 10.27am (4.27pm).

Police revealed Hale had drawn a detailed map of the school, which included potential entry points and had planned surveillance before killing their victims.

Nashville police chief John Drake said they are reviewing a manifesto and writings from the assailant whom they called a "lone zealot".

Mr Drake said: "We have a manifesto, we have some writings that we're going over that pertain to this date, the actual incident. We have a map drawn out of how this was all going to take place."

Mr Drake told NBC News that investigators believed the shooting stemmed from "some resentment" Hale harboured "for having to go to that school" when they were younger.

However, no definitive motive has yet been given for Hale's actions.