Nashville school shooting (Audrey Hale)

New details continue to emerge about the 28-year-old suspect accused of shooting dead three nine-year-old children and three staff members in a devastating mass shooting at a christian elementary school in Nashville on Monday morning.

Audrey Hale, a former student, allegedly entered The Covenant School in Nashville, Tennessee, just after 10am.

Inside, the shooter opened fire on students and staff, killing six victims.

Students Evelyn Dieckhaus, Hallie Scruggs, and William Kinney, all aged nine, Head of School Katherine Koonce, 60, Cynthia Peak, 61, and Mike Hill, 61, all died in the attack.

Two responding police officers shot the suspect dead.

Nashville police said on Monday the shooter was 28-year-old Audrey Elizabeth Hale.

Police have identified the suspected shooter by their name at birth; Hale reportedly was a transgender man who used he/him pronouns, though law enforcement officials initially described the suspect as a woman in the aftermath of the shooting. Police did not provide another name but on the suspect’s social media accounts they refer to themselves as Aiden.

Metro Nashville Police Chief John Drake said in a press conference on Monday that Hale once attended the christian elementary school.

An illustrator and graphic designer who attended Nossi College of Art, Hale had no criminal record prior to Monday’s massacre and was not known to law enforcement.

During a press conference on Tuesday, Chief Drake said investigators discovered Hale had been treated for mental health challenges prior to the shooting.

The police chief said that Hale’s parents were aware the suspect had purchased one firearm, but believed it had since been sold.

In reality, the 28-year-old had legally purchased seven firearms from five different local stores – three of which were used in Monday’s shooting – and hid them in the family home.

It’s just tragic. The sweet children that were hurt and killed, the adults. All of it.”

The shooter is seen stalking the school corridors with a gun with a long barrel, including walking into a room labelled “church office”, then coming back out.

Police said Hale opened fire on students and staff, killing six.

The first call to 911 about shots being fired came in at 10.13am, police said.

When officers rushed to the campus, the shooter opened fire on arriving police cars from a window on the second floor.

Chief Drake said at a Tuesday press conference that investigators “believe there has been some training to have been able to shoot from a higher level” down onto the officers.

Officers entered the building and began clearing the building, police said.

While clearing the building, officers heard shots fired on the second level and moved to the second floor common area where they encountered Hale, fatally shooting the assailant, police said.

Bodycam footage, released on Tuesday morning, captured the officers searching for the shooter in the school.

The officers move from classroom to classroom, clearing each room while searching for the assailant, as sirens emergency alarms ring out overheard.

While clearing the rooms, gunshots are heard being fired elsewhere in the elementary school building.

The officers then encounter Hale in front of a window in the atrium on the second floor of the school.

The 28-year-old former student is then shot dead by two veteran officers.

Monday’s tragedy unfolded over roughly 14 minutes.

The shooter had drawn a detailed map of the building and conducted surveillance before carrying out the massacre, police said.

"We have a manifesto, we have some writings that we're going over that pertain to this date, the actual incident," the police chief told reporters on Monday. "We have a map drawn out of how this was all going to take place."

He said in an interview with NBC News that investigators believe the killer had "some resentment for having to go to that school".

Writings recovered from Hale also revealed that the attack was calculated and planned.

Hale’s chilling final messages have now come to light, issuing a dark warning to a friend that “something bad is about to happen” just minutes before the shooting unfolded.

Hale sent a series of direct messages to friend Averianna Patton via Instagram on Monday morning.

In the harrowing messages sent at 9.57am, Hale revealed plans to die by suicide telling Ms Patton “this is my last goodbye” and that she would soon be reading about it “on the news after I die”.

“One day this will make more sense,” Hale wrote.

Just 16 minutes later – at 10.13am – law enforcement received the first 911 call reporting shots fired inside The Covenant School.