Audrey Elizabeth Hale was killed by police following the massacre at The Covenant School in state capital Nashville on Monday morning.
Hale was later found to have drawn a detailed map of the school, including potential entry points, and had carried out surveillance of the building before the killing spree, police said.
Late on Monday night, police released approximately two minutes of edited CCTV footage showing Hale’s car driving up to the school from multiple angles, including one in which children can be seen playing on swings in the background.
Hale arrived at the school in a Honda Fit, heavily armed with two assault-type weapons and a handgun.
Next, an interior view shows glass doors to the school being shot out and Hale ducking through one of the shattered doors.
More footage from inside shows the shooter prowling through a school corridor holding a gun with a long barrel and walking into a room labelled “church office,” before re-emerging.
In the final part of the footage, Hale can be seen walking down another long corridor with the gun drawn. Hale is not seen interacting with anyone else on the video, which has no sound.
The victims included three nine-year-old children, the school’s top administrator, a substitute teacher and a custodian.
The child victims were identified as Evelyn Dieckhaus, Hallie Scruggs, and William Kinney.
They were killed along with substitute teacher Cynthia Peak, 61; Katherine Koonce, 60, who is believed to have been the school’s head; and Mike Hill, 61, reportedly a custodian.
Metropolitan Nashville Police Chief John Drake gave chilling examples of the shooter’s elaborate planning for the targeted attack.
“We have a manifesto, we have some writings that we’re going over that pertain to this date, the actual incident,” he told reporters.
“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 Hale had “some resentment for having to go to that school.”
A series of final messages were reportedly sent by Hale on Monday to a former basketball teammate saying “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 in messages shared by the friend with NewsChannel5.
“I’ve left behind more than enough evidence behind. But something bad is about to happen”, she reportedly wrote.
The friend told NewsChannel5 that she contacted the Suicide Prevention Help Line at 10.08am to try to get Hale help.
“Audrey has shared with others that she had been suicidal in the past and I knew to take this serious,” she told NewsChannel 5.
Monday’s tragedy unfolded over roughly 14 minutes.
Police received the initial call about an active shooter at 10.13am. Officers began clearing the first story of the school when they heard gunshots coming from the second level, police spokesperson Don Aaron said.
Police later said the shooter fired at arriving officers from a second-story window and had come armed with significant ammunition.
Two officers from a five-member team opened fire in response, shooting Hale dead at 10.27am, Mr Aaron said.
Mr Aaron said there were no police officers present or assigned to the school at the time of the shooting because it is a church-run school.
Following the tragedy, panicked parents rushed to the school to see if their children were safe, and a stunned community held vigils for the victims.
Rachel Dibble, who was at a nearby church where children were taken to be reunited with their parents, described the scene as everyone being in “complete shock.”
“People were involuntarily trembling,” she said. “The children...started their morning in their cute little uniforms, they probably had some Froot Loops and now their whole lives changed today.”
Police initially identified the shooter as a woman, but said in a press conference late on Monday afternoon that Hale was transgender. After the news conference, police spokesperson Mr Aaron declined to elaborate on how Hale identified.
Authorities said Hale was armed with two “assault-style” weapons and a handgun. At least two of them were believed to have been obtained legally in the Nashville area, according to the chief.
Police said a search of Hale’s home also turned up a sawed-off shotgun and a second shotgun.
Founded as a ministry of Covenant Presbyterian Church, The Covenant School is located in the affluent Green Hills neighbourhood just south of central Nashville that is home to the famed Bluebird Café - a spot typically beloved by musicians and songwriters.
The school has around 200 students including nursery-aged youngsters, as well as roughly 50 staff members.
“Our community is heartbroken,” a statement from the school said. “We are grieving tremendous loss and are in shock coming out of the terror that shattered our school and church
“ We are focused on loving our students, our families, our faculty and staff and beginning the process of healing.”
President Joe Biden, speaking at the White House on Monday, called the shooting a “family’s worst nightmare” and implored Congress again to pass a ban on certain semi-automatic weapons.
A reeling city mourned during multiple vigils Monday evening. At Belmont United Methodist Church, the sounds of crying filled the background as vigil attendees sang, knelt in prayer and lit candles.
The incident is the latest in a series of mass shootings in the US. Just last week alone, school shootings happened in Denver and the Dallas-area within two days of each other.