NASHVILLE: The former student of a Christian grade school in Nashville who killed three 9-year-olds and three adults in a shooting spree there was under a doctor's care for an "emotional disorder" and had amassed a collection of guns, the city's police chief said on Tuesday.

New details about assailant Audrey Elizabeth Hale, 28, emerged hours after police released harrowing video showing officers storming the Covenant School in the midst of Monday's rampage and conducting a room-to-room search before confronting and fatally shooting Hale.

Authorities said they were still trying to pin down a motive as detectives pored over various writings and other evidence left by Hale.

Hale was armed with two assault-style weapons and a handgun, the latest in a long string of U.S. mass shootings that have turned schools into killing zones and added fuel to a national debate over gun rights and regulations.

The three weapons used on Monday were among seven firearms that Hale had legally purchased in recent years from five Nashville-area stores, Metropolitan Nashville Police Chief John Drake told reporters on Tuesday.

Hale's own parents did not know that Hale possessed multiple firearms, mistakenly believing that Hale had owned just one gun, then sold it, Drake said. The chief added that the mother and father felt Hale should not have owned any weapons due to mental health concerns.

The mother, on seeing Hale leave the house with a red bag Monday morning, had questioned what was in the bag, the chief said.

Hale "was under care, a doctor's care, for an emotional disorder," the chief told reporters during a news briefing, without elaborating.

Under Tennessee law, mental illness is not grounds for police to confiscate weapons, unless a person is deemed mentally incompetent by a court, "judicially committed" to a mental institution," or placed under a conservatorship "by reason of mental defect."

Tennessee prohibits selling guns to persons found by a court or other legal authority to pose a danger to themselves or others, or lack the capacity to conduct their own affairs due to mental illness. But merely being under a doctor's care would not, in itself, meet that threshold.

Drake said it appeared Hale had some sort of weapons training. Hale fired on officers from the school's second floor as they arrived in patrol cars while standing back from large windows to avoid becoming an easy target.

MANIFESTO AND UNANSWERED QUESTIONS

Hale left behind a detailed map of the school showing entry points as well as what Drake described as a "manifesto" indicating that Hale may have planned to carry out shootings at other locations.

On Monday, Drake said Hale identified as a transgender person, and said investigators believe the suspect harbored "some resentment for having to go to" the Covenant School as a child.

The chief declined to elaborate and did not say what role, if any, Hale's gender identity, educational background or other social or religious dynamics might have played. Investigators "don't have a motive at this time," he said Tuesday.

The shooting came weeks after Tennessee's legislature thrust the state to the forefront of a political furor over LGBTQ rights by voting to ban gender-affirming medical treatments for transgender children and to place new restrictions on drag performances.

The suspect's LinkedIn page, listing recent jobs in graphic design and grocery delivery, showed Hale preferred male pronouns.

VIDEO FOOTAGE

The six minutes of video footage released on Monday, edited together from the body-worn cameras of two responding officers, offered a glimpse of the rampage as it unfolded. The video opens with an officer retrieving a rifle from his trunk as a staff member tells him the school is locked down but two children are unaccounted for.

"Let's go! I need three!" the officer yells as he enters the building, where alarms can be heard ringing.

The video shows officers clearing one room after another before heading upstairs, where one says, "We've got one down."

Amid the sound of gunfire, the officers race down the hallway - past what appears to be a victim lying on the ground - and into a lounge area, where the suspect is seen dropping to the floor after being shot.

The two officers whose body-worn cameras provided the footage both fire several rounds at the suspect. The video shows the assailant still moving on the floor as another officer repeatedly yells, "Get your hands away from the gun!"

According to a police timeline of the incident, just 14 minutes elapsed from the first reports of a shooting to police neutralizing the suspect.

Monday's violence marked the 90th school shooting – defined as any incident in which a gun is discharged on school property – in the United States this year, according to the K-12 School Shooting Database, a website founded by researcher David Riedman. Last year saw 303 such incidents, the highest of any year in the database, which goes back to 1970.

The three children killed on Monday were identified as Evelyn Dieckhaus, Hallie Scruggs and William Kinney. The three adults killed were Katherine Koonce, 60, the head of school; Mike Hill, 61, a custodian; and Cynthia Peak, 61, a substitute teacher.

The Covenant School, founded in 2001, serves about 200 students from preschool to sixth grade in the Green Hills neighborhood of Tennessee's state capital, according to the school's website.