NASHVILLE, Tenn. >> A former student shot through the doors of a Christian elementary school and killed three children and three adults after elaborately planning the massacre by drawing out a detailed map and conducting surveillance of the building, police said.

The massacre at The Covenant School in Nashville was the latest in a series of mass shootings in a country that has grown increasingly unnerved by bloodshed in schools.

The victims included three 9-year-old children, the school’s top administrator, a substitute teacher and a custodian. Amid the chaos a familiar ritual played out: Panicked parents rushed to the school to see if their children were safe and tearfully hugged their kids, and a stunned community planned vigils for the victims.

“I was literally moved to tears to see this and the kids as they were being ushered out of the building,” Metropolitan Nashville Police Chief John Drake said Monday during one of several news conferences.

Police gave unclear information on the gender of the shooter. For hours, police identified the shooter as a 28-year-old woman and eventually identified the person as Audrey Hale. Then at a late afternoon press conference, the police chief said that Hale was transgender. After the news conference, police spokesperson Don Aaron declined to elaborate on how Hale currently identified.

Drake did not give a specific motive when asked by reporters but gave chilling examples of the shooter’s prior planning for the targeted attack.

“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.”

He said in an interview with NBC News that investigators believe Hale had “some resentment for having to go to that school.”

The shooter gained entry by firing into glass doors on the building, shattering them, police later said in a tweet.

The shooter was armed with two “assault-style” weapons as well as a handgun, authorities said. At least two of them were believed to have been obtained legally in the Nashville area, according to the chief.

The victims were identified as Evelyn Dieckhaus, Hallie Scruggs, and William Kinney, all 9 years old, and adults 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.

Students held hands as they walked to school buses, which drove them to a nearby church to be reunited with their parents.

Rachel Dibble, who was at the church as families found their children, described the scene as everyone being in “complete shock.”

“People were involuntarily trembling,” said Dibble, whose children attend a different private school in Nashville. “The children … started their morning in their cute little uniforms, they probably had some Froot Loops and now their whole lives changed today.”

Communities around the U.S. has suffered through one mass killing after another in recent years, with school shootings taking an especially painful toll.

Recent tragedies nationwide include the massacre at an elementary school in Uvalde, Texas, last year; a first grader who shot his teacher in Virginia; and a shooting last week in Denver that wounded two administrators.

President Joe Biden, speaking at the White House on Monday, called the shooting a “family’s worst nightmare” and implored Congress again to pass a ban on certain semi-automatic weapons.

“It’s ripping at the soul of this nation, ripping at the very soul of this nation,” Biden said.

Biden later ordered the U.S. flag to be flown at half-staff on all federal buildings through March 31. He also spoke to Tennessee Gov. Bill Lee and Nashville Mayor John Cooper about the shooting, officials said.

Founded as a ministry of Covenant Presbyterian Church — which is affiliated with the conservative evangelical Presbyterian Church in America — The Covenant School is located in the affluent Green Hills neighborhood just south of downtown Nashville that is home to the famed Bluebird Café – a spot typically beloved by musicians and songwriters.

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

“Our community is heartbroken,” a statement from the school said. “We are grieving tremendous loss and are in shock coming out of the terror that shattered our school and church. We are focused on loving our students, our families, our faculty and staff and beginning the process of healing.”

Before Monday’s violence in Nashville, there had been seven mass killings at K-12 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 tragedy unfolded over roughly 14 minutes. Police received the initial call about an active shooter at 10:13 a.m.

Officers began clearing the first story of the school when they heard gunshots coming from the second level, Aaron said during a news briefing. Police later said in a tweet that the shooter fired at arriving officers from a second-story window and had come armed with significant ammunition.

Two officers from a five-member team opened fire in response, fatally shooting the suspect at 10:27 a.m., Aaron said. One officer had a hand wound from cut glass.

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

Jozen Reodica heard the police sirens and fire trucks blaring from outside her office building nearby. As her building was placed under lockdown, she took out her phone and recorded the chaos.

“I thought I would just see this on TV,” she said. “And right now, it’s real.”

Nashville has seen its share of mass violence in recent years, including a Christmas Day 2020 attack where a recreational vehicle was intentionally detonated in the heart of Music City’s historic downtown, killing the bomber, injuring three others and forcing more than 60 businesses to close.

A reeling city mourned during multiple vigils Monday evening. At Belmont United Methodist Church, teary sniffling filled the background as vigil attendees sang, knelt in prayer and lit candles. They lamented the national cycle of violent and deadly shootings, at one point reciting together, “we confess we have not done enough to protect” the children injured or killed in shootings.

“We need to step back. We need to breathe. We need to grieve,” said Paul Purdue, the church’s senior pastor. “We need to remember. We need to make space for others who are grieving. We need to hear the cries of our neighbors.”

Contributing to this report were Associated Press writers Holly Meyer and Kristin Hall in Nashville; Denise Lavoie in Richmond, Virginia; John Raby in Charleston, West Virginia; Stefanie Dazio in Los Angeles; and Beatrice Dupuy and Larry Fenn in New York.