Nashville police have released video from a body camera that shows a team of officers entering and searching an elementary school, then confronting and opening fire on an assailant who had murdered three children and three adults in the latest school shooting to roil the United States.

The dramatic, six-minute video supplements an earlier release of about two minutes of edited surveillance footage that shows the shooter’s car driving up to the school, glass doors being shot out and the shooter ducking through one of them.

The new video from Officer Rex Engelbert’s body cam shows a woman greeting police outside as they arrive at The Covenant School on Monday. “The kids are all locked down, but we have two kids that we don’t know where they are,” she tells police.

“Okay, yes, ma’am,” Engelbert replies.

Bodycam footage of police responding to an active shooting at The Covenant School in Nashville, Tennessee. Photo / Metropolitan Nashville Police Department via AP

The woman then directs officers to Fellowship Hall and says people inside had just heard gunshots. “Upstairs are a bunch of kids,” she says.

Three officers, including Engelbert, search rooms one by one, holding rifles. “Metro Police,” officers yell.

“Let’s go, let’s go,” one officer yells.

As alarms are heard going off in the school, one officer says, “It sounds like it’s upstairs.”

Police responded after a former student shot through the doors of the Christian elementary school and killed three children and three adults. Photo / Metropolitan Nashville Police Department via AP

Officers climb stairs to the second floor and enter a lobby area. “Move in,” an officer yells. Then a barrage of gunfire is heard.

“Get your hands away from the gun,” an officer yells twice. Then the shooter is shown motionless on the floor.

Police earlier identified the shooter, who was killed by police, as 28-year-old Audrey Elizabeth Hale. They say Hale was a former student and shot through the doors of the private, Christian elementary school. Hale had drawn a detailed map of the school, including potential entry points, and conducted surveillance of the building before carrying out the massacre, authorities said.

A screen grab from surveillance video tweeted by the Metropolitan Nashville Police Department shows Audrey Elizabeth Hale pointing an assault-style weapon inside The Covenant School. Photo / Metropolitan Nashville Police Department via AP

Police have given unclear information on Hale’s gender. For hours Monday, police identified the shooter as a woman. At a late afternoon press conference, the police chief said Hale was transgender. After the news conference, police spokesman Don Aaron declined to elaborate on how Hale identified.

In an email Tuesday, police spokeswoman Kristin Mumford said Hale “was assigned female at birth. Hale did use male pronouns on a social media profile.”

The victims were Evelyn Dieckhaus, Hallie Scruggs and William Kinney, all age 9. The adults were Cynthia Peak, 61, Katherine Koonce, 60, and Mike Hill, 61.

The website of The Covenant School, a Presbyterian school founded in 2001, lists a Katherine Koonce as the head of the school. Her LinkedIn profile says she has led the school since July 2016. Peak was a substitute teacher, and Hill was a custodian, according to investigators.

A child on a bus leaving The Covenant School following a mass shooting. Photo / Nicole Hester, The Tennessean via AP

Metropolitan Nashville Police Chief John Drake did not say exactly what drove Hale but said in an interview with NBC News that investigators believe the shooter had “some resentment for having to go to that school”.

Drake provided chilling examples of the shooter’s elaborate planning for the targeted attack, the latest in a series of mass shootings in a country that has grown increasingly unnerved by bloodshed in schools.

“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.”

Authorities said Hale was armed with two “assault-style” weapons, as well as 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 turned up a sawn-off shotgun, a second shotgun and other unspecified evidence.

US President Joe Biden again called on lawmakers for stronger gun safety laws.

“It is time to show some courage here,” White House press secretary Karine Jean-Pierre said Tuesday on CNN. “It is time for Republicans in Congress to show some courage and to answer to these parents, to these families.”

President Joe Biden has called on Congress again to pass his assault weapons ban after the Nashville shooting. Photo / Alex Brandon, AP

Founded as a ministry of Covenant Presbyterian Church, The Covenant School is in the affluent Green Hills neighborhood just south of downtown Nashville that is home to the famous Bluebird Cafe, beloved by musicians and songwriters.

The school has about 200 students from preschool through sixth grade, as well as roughly 50 staff members.

Before Monday’s violence in Nashville, there had been seven mass killings at Year 1-Year 8 schools since 2006 in which four or more people were killed within a 24-hour period, according to a database maintained by The Associated Press and USA Today in partnership with Northeastern University. In all of them, the shooters were males.

The database does not include school shootings in which fewer than four people were killed, which have become far more common in recent years. Just last week alone, for example, school shootings happened in Denver and the Dallas area within two days of each other.

Monday’s shooting unfolded over roughly 14 minutes. Police received the initial call about an active shooter at 10.13am. Police killed the suspect at 10.27am.

Officers began clearing the first storey of the school when they heard gunshots coming from the second level, Aaron said. Police later said the shooter fired at arriving officers from a second-storey window.

Police identified Engelbert, a four-year member of the force, and Collazo, a nine-year member, as the officers who fatally shot Hale.

A woman and child bring flowers to lay at the entry to Covenant School which has become a memorial for shooting victims. Photo / AP

The surveillance video released Monday shows the shooter’s car driving up to the school from multiple angles, including one in which children can be seen playing on swings in the background. Next, an interior view shows glass doors to the school being shot out and the shooter ducking through one of the shattered doors.

More footage from inside shows the shooter walking through a school corridor holding a gun with a long barrel and walking into a room labelled “church office”, then coming back out. In the final part of the footage, the shooter can be seen walking down another long corridor with the gun drawn. The shooter is not seen interacting with anyone else on the video, which has no sound.

Aaron said no police officers were present or assigned to the school at the time of the shooting because it is a church-run school.

- Jonathan Mattise, Travis Loller and Holly Meyer, AP