The US police said that the woman who killed six people at a school in Nashville, Tennessee, on Monday legally purchased seven guns and hid them at home.

Investigators say the parents of the suspect, 28-year-old Audrey Hill, believed she should not have had guns and did not realize the weapons were hidden in their home.

The incident led to the deaths of six people, including three children as young as nine, in the attack on the Covenant Christian Private School.

Police say the suspect was receiving "a doctor's care for an emotiona

There are no laws in Tennessee that allow police to confiscate weapons from violent suspects.

Although there are no so-called red flag laws, police said they would have sought to confiscate the weapons if authorities had had any warning that the suspect might pose a threat.

The pupils killed in the attack were Evelyn Dickhouse, Haley Scruggs and William Kenny.

Three adult staff members of the privately run Christian school also died: Cynthia Beck, 61, Kathryn Consey, 60, and Mike Hill, 61.

Police spoke to the parents of suspect Audrey Hill, who was killed by police less than 15 minutes after the attack began

 shooter, Hale, who is known to be transgender and was a former student at the school, carried three rifles, including a semi-automatic rifle.

The attack took place after the killer surveyed the building, drew maps and wrote what police described as a "manifesto".

Hill's parents believed the suspect had only one gun, but it had been sold.

Nashville Police Chief John Drake said on Tuesday that they believed the suspect "should not have had weapons" and did not know she "was hiding multiple weapons inside the house."

The guns were purchased legally from five stores across the city.

Drake said the killer was "under the care - the care of a doctor - because of an emotional disorder", without providing further details.

He added that if there had been reports of suicidal or violent tendencies, the police would have sought to confiscate the weapons.

"But in the current situation, we had absolutely no idea who this person was or even if (the suspect) was there," he said 

The police received the first call about the incident at 10:13 local time on Monday.

The suspect arrived at the school in a Honda Fit and entered the building after the shooting through one of the doors, which were all locked.

Video footage later released by Nashville police shows the shooter opening fire to shatter the glass panels on the front doors, then wandering the school's empty hallways, and at one point walking past a room called the "Children's Ministry
In other CCTV footage, the suspect is wearing what appears to be a protective vest and holding an assault rifle in one hand, with a second weapon visible slung from her left thigh.

The suspect opened fire on the ground floor before moving to the second floor of the building.

As the police cars arrived, the suspect fired at the police from the second floor, hitting the windshield of one of the cars