A heavily armed 28-year-old fatally shot three children and three adult staff at a private Christian school the suspect once attended in the US city of Nashville before police killed the assailant, authorities said.
The motive was not immediately known, but the suspect had drawn detailed maps of the school, including entry points for the building, and left behind a "manifesto" and other writings that investigators were examining, Police Chief John Drake told reporters.
The latest in an epidemic of deadly mass gun violence that has come to routinely terrorise even the most cherished of US institutions unfolded on a warm spring morning at The Covenant School, whose students consist mostly of elementary school-age children.
Mr Drake identified the suspect as Audrey Elizabeth Hale, 28, a resident of the Nashville area, and referred to the assailant by female pronouns.
The chief said the suspect identified as transgender but provided no further clarity.
Later, the Tennessean newspaper cited a police spokesperson as saying Hale used he/him pronouns.
Hale used male pronouns on a LinkedIn page that listed recent jobs in graphic design and grocery delivery.
Addressing a news conference, Mr Drake said police were working on a theory about what may have precipitated the shooting and would "put that out as soon as we can." He said the suspect had no known prior criminal history.
In a subsequent NBC News television interview, Mr Drake said investigators believed the shooting stemmed from "some resentment" the suspect harboured "for having to go to that school" as a younger person.
The police chief did not specify the nature of such presumed resentment, or whether it had anything to do with the suspect's gender identity or the Christian orientation of the school.
Mr Drake said the school was singled out for attack but the individual victims were targeted at random.
'Swift' police response
The Metropolitan Nashville Police Department began receiving calls at 10.13am (local time) of a shooter at the school, and arriving officers reported hearing gunfire coming from the building's second floor, police spokesperson Don Aaron told reporters.
Two officers from a five-member team shot the assailant in a lobby area, and she was pronounced dead by 10.27am (local time).
"The police department's response was swift," Mr Aaron said.
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Mr Drake said the suspect, who was armed with a semi-automatic rifle and two handguns, had previously been a student at the school.
The attacker gained entry to the school by firing through one of the doors, the chief said.
Three students were pronounced dead after arriving at Monroe Carell Jr. Children's Hospital at Vanderbilt with gunshot wounds, hospital spokesperson John Howser said in a statement.
Three adult staff members were killed by the shooter, police said.
The victims were later identified as Evelyn Dieckhaus, Hallie Scruggs, and William Kinney, all age 9, along with staff Mike Hill, 61, a school custodian, Cynthia Peak, 61, substitute teacher, and Katherine Koonce, 60, listed on the Covenant website as "head of school."
Besides the deceased, no one else was shot, Mr Aaron said.
Reacting in Washington to the latest school shooting, US President Joe Biden urged the US Congress again to pass tougher gun reform legislation.
"It's sick," Mr Biden said, addressing the issue during an event at the White House and urging Congress again to pass a ban on assault-style weapons.
"We have to do more to stop gun violence. It's ripping our communities apart, ripping the soul of this nation."
US Senator Marsha Blackburn, a Tennessee Republican, said on Twitter that her office stands "ready to assist" those affected by the shooting.
But Rosanne Cash, daughter of Nashville country music icon Johnny Cash and a singer-songwriter in her own right, responded by criticising Ms Blackburn's ties to the National Rifle Association (NRA) gun lobby.
"You vote against every common sense gun control bill that comes across your desk, you've taken over $1 million from the NRA and you rank 14th in all Congress for NRA contributions. Spare us the hand-wringing," Ms Cash tweeted.
At the state level, Tennessee in 2021 did away with its permit requirement for carrying a concealed handgun and now allows anyone aged 21 and older to carry a firearm, either openly or concealed, without a permit, as long as they are legally allowed to purchase the weapon.
Possessing a handgun is outlawed in Tennessee for anybody who has been convicted of a felony offence involving violence or drugs.
Students' parents were told to gather at the nearby Woodmont Baptist Church to be reunited with their children.
Parents trickled out of the building with their youngsters in tow.
One woman was visibly distraught as she was escorted alone out of the church to a waiting squad car by police officers who said they were headed to Vanderbilt.
The Covenant School, founded in 2001, is a ministry of Covenant Presbyterian Church in the Green Hills neighbourhood of Nashville with about 200 students, according to the school's website.
The school serves preschool through sixth graders and held an active shooter training programme in 2022, WTVF-TV reported.
Nashville Mayor John Cooper expressed sympathy for the victims and wrote on social media that his city "joined the dreaded, long list of communities to experience a school shooting."
There have been 89 school shootings – defined as any incident in which a gun is discharged on school property – in the US so far in 2023, 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.
