The 28-year-old who shot dead six people at an elementary school in Nashville was able to buy and conceal multiple weapons in the family home despite evidence of mental health issues, police said Tuesday.

Two nine-year-old girls, a nine-year-old boy, two teachers and a school custodian died in the Monday attack, which recharged the bitter debate over gun rights in the United States.

Parents with their children joined a steady stream of mourners in front of a makeshift memorial to the victims of the massacre at the Covenant School in Nashville as the sun set Tuesday, many of them in tears.

"It's just unimaginable to think that these beautiful kids are not going to come home again," Lisbeth Melgar, who brought her two children to see the memorial, told AFP as she gently tucked her daughter's hair behind her ear.

Earlier, Nashville police chief John Drake told reporters that the shooter, Audrey Hale, had been receiving treatment for an "emotional disorder," and that Hale's parents believed their child -- who lived at home with them -- had bought and later resold a single gun.

But Hale, who was killed during the attack, was armed with two assault rifles and a handgun upon entering the small Christian academy of about 200 students, which the shooter had once attended as a pupil.

Identified by police as a female who had used male pronouns on social media, the shooter had maps of the school and left a manifesto that suggested more attacks were planned.

"Audrey bought seven firearms from five different local gun stores here legally," Drake said.

"She was under doctors' care for an emotional disorder... Her parents felt that she should not own weapons."

"As it turned out, she had been hiding several weapons within the house," he continued.

Drake added that pupils and staff were not targeted individually and there was no known motive.

Video of police response

In security camera footage, Hale is seen shooting through doors to enter the school before stalking the empty halls as emergency lights flash.

Hale, wearing a black military-style vest, camouflage pants and red baseball cap, moved through the building, opening fire on children and staff.

Officers were on the scene within about 15 minutes of the first emergency call.

Bodycam footage showed police moving through classrooms filled with small desks and paper craftwork.

Multiple gunshots are heard as officers close in on a sun-filled atrium, where the assailant was shot dead.

A former schoolmate, Averianna Patton, told CNN Hale sent an Instagram message the morning of the shooting.

"One day this will make more sense," Hale wrote. "I've left more than enough evidence behind. But something bad is about to happen."

Patton said she called police to alert them at about the time the attack started.

In the search for a motive, Drake told NBC News that "there's some belief that there was some resentment for having to go to that school."

One of the young children killed was Hallie Scruggs, the daughter of the church's pastor, Chad Scruggs.

"We are heartbroken. She was such a gift," the pastor told local media.

Gun rights

Asked whether Hale's gender identity may have been a factor, police said they were investigating all leads.

A rally that had been scheduled for Friday supporting queer and trans youth in Nashville was cancelled "both for the safety of the youth and to focus on the healing of the Nashville community," according to an email sent by organizers.

Mourners left flowers and stuffed toys at the growing memorial outside the school. Some knelt in prayer.

"I carry a gun with me most days, but I don't need an assault rifle," Chad Baker, 44, told AFP. "I don't think it should be as easy to buy flowers as it is a gun."

There were more than 24 million AR-15-style assault weapons circulating in the United States by mid-2022, according to the NSSF firearm trade association.

President Joe Biden warned that gun violence was "ripping the soul of this nation," and urged Congress to reinstate the national assault rifle ban, which existed from 1994 to 2004.

Efforts to ban the powerful weapons have run up against opposition from Republicans, staunch defenders of the constitutional right to bear arms.

The political deadlock endures despite an uproar over recurring school massacres, including last year when a shooter in Uvalde, Texas, killed 19 students and two teachers.

Last year also marked 10 years since 26 people, mostly children, were killed at Sandy Hook elementary school in Connecticut -- deeply shocking the nation, yet failing to produce meaningful gun control.

Without that progress, many schools have turned to security measures such as metal detectors and active shooter drills instead.

"It's not on schools to figure out more security," said Nina Dyson, a mother of four attending a small demonstration in Nashville Tuesday seeking gun control.

"There are parents all over the country demanding change for decades, and there (has) been none," the 35-year-old said at the protest, which had been planned before Monday's attack took place.

© Agence France-Presse