Six persons, including three nine-year-old children, were killed on Monday in a shooting at a private school in United States’ Nashville city, reported CNN.

The shooter, identified as 28-year-old Audrey Hale, was shot dead by the law enforcement agencies. Metro Nashville Police said that Hale was armed with two assault rifles and a handgun. The incident took place at The Covenant School, a Christian academy.

“We’ve also determined that there were maps drawn of the school in detail of – surveillance, entry points, et cetera,” Metro Nashville Police Chief John Drake at a press conference. “We know and believe entry was gained through shooting through one of the doors, is how they actually got into the school.”

The police have identified Hale as a transgender person.

“We have a manifesto, we have some writings that we’re going over that pertain to this date, the actual incident,” he said. “We have a map drawn out of how this was all going to take place.”

Investigators believe that Hale had some resentment for having to go to that school, Drake told NBC News.

Several incidents of mass shootings in the US have been reported over the years, including at schools.

Last week, seven persons were killed in two separate shootings in northern California.

In May, 19 children and two teachers were killed Uvalde city of Texas state. This was one of the deadliest attacks at an American school since a gunman killed 26 people, including 20 children, in a rampage at Sandy Hook Elementary School in Connecticut in 2012.

Monday’s incident is the 129th mass shooting in 2023, according to US-based non-profit organisation The Gun Violence Archive.

Meanwhile, US President Joe Biden called the shooting a family’s worst nightmare.

“We have to do more to stop gun violence,” Biden said. “It’s ripping our communities apart, ripping at the very soul of the nation. And we have to do more to protect our schools so they aren’t turned into prisons.”