Inside the horrifying Nashville school shooting

Officer Rex Engelbert, whose body camera footage revealed a torturous blow-by-blow of the closing moments of the Nashville school shooting that left three nine-year-old children and three staff members dead, hurried inside after being allowed in by another employee.

After being shot by police on the second story of the Covenant school, the 28-year-old accused killer Audrey Hale was found dead minutes later.

The astonishing recordings, which depict the officers sprinting along halls laden with children's jackets and bags before their meeting with the gunman, startled a nation that is once more searching for explanations in the wake of another mass killing.

As more information about Audrey Hale, comes to light, investigators are still looking for a possible motivation.

According to Chief John Drake of the Metro Nashville Police Department, Hale was a former student who had been receiving treatment for an "emotional disorder." Law enforcement also discovered that Hale had written notes that seemed to indicate the attack had been meticulously planned out in advance.

The incident started at 10:10 am, local time, on Monday when Hale entered the building through a side entrance.

What follows is captured on surveillance footage from within the school: a hail of gunfire causes glass doors to break, allowing the heavily armed attacker to enter.

The suspect opened fire on the policemen when they arrived from an upper window, injuring at least one police vehicle.

Investigators believe the suspect had some training to be able to fire from an elevated position while standing back from the window to avoid being "an easy target."

The footage reveals that Officer Engelbert first came into contact with the shooter after turning into an atrium from the direction in which Hale appeared to be firing.

Hale is hit by four bullets from him and crumples to the ground. Four more rounds are fired by other police as they order the assailant to halt moving. The shooter then remains unmoving in front of the atrium glass as his guns are taken away.

The 14 minutes of terror included blaring alarms, as heard in body cam footage of police officers. Within a few minutes, six victims had died and the shooter too was shot down by brave officers.