NASHVILLE, Tenn. — The shooter who killed three students and three staff members at a Christian school in Nashville legally bought seven weapons in recent years and hid the guns from their parents before carrying out the attack by firing indiscriminately at victims and spraying gunfire through doors and windows, police said Tuesday.

The violence Monday at The Covenant School was the latest school shooting to roil the nation and was planned carefully. The shooter 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.

The suspect, Audrey Hale, 28, was a former student at the school. Hale did not target specific victims — among them three 9-year-olds and the head of the school — but did target "this school, this church building," police spokesperson Don Aaron said at a news conference Tuesday.

Hale was under a doctor's care for an undisclosed emotional disorder and was not known to police before the attack, Metropolitan Nashville Police Chief John Drake said at the news conference.

If police had been told that Hale was suicidal or homicidal, "then we would have tried to get those weapons," Drake said. "But as it stands, we had absolutely no idea who this person was or if (Hale) even existed."

Hale legally bought seven firearms from five local gun stores, Drake said. Three of them were used in Monday's shooting.

Hale's parents believed their child had sold one gun and did not own any others, Drake said, adding that Hale "had been hiding several weapons within the house."

Hale's motive is unknown, Drake said. In an interview with NBC News on Monday, Drake said investigators don't know what drove Hale but believe the shooter had "some resentment for having to go to that school."

Drake, at Tuesday's news conference, described "several different writings by Hale" that mention other locations and The Covenant School. There also was a map of the school and a drawing about how Hale would potentially enter the school.

"There's quite a bit of writing to it," he said.

Police have released videos of the shooting, including 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.

Additional video, from Officer Rex Engelbert's bodycam, shows a woman greeting police outside as they arrive at The Covenant School on Monday and telling them that all the children were locked down, "but we have two kids that we don't know where they are."

The woman then directs officers to Fellowship Hall and says people inside had just heard gunshots. Three officers, including Engelbert, search rooms one by one, holding rifles and announcing themselves as police.

The video shows officers climbing stairs to the second floor and entering a lobby area, followed by a barrage of gunfire and an officer yelling twice: "Get your hands away from the gun." Then the shooter is shown motionless on the floor.

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

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.

Police response times to school shootings have come under greater scrutiny after the attack in Uvalde, Texas, in which 70 minutes passed before law enforcement stormed the classroom. In Nashville, police have said 14 minutes passed from the initial call to when the suspect was killed, but they have not said how long it took them to arrive.

Surveillance video shows a time stamp of just before 10:11 a.m., when the attacker shot out the doors. Police said they got the call about a shooter at 10:13 a.m. but have not said precisely what time they arrived, and the edited bodycam footage didn't include time stamps. A police spokesperson didn't respond to an email Tuesday asking when they arrived or whether any version of the video includes time stamps.

During the news conference, Drake did not answer a question directly about how many minutes it took police to arrive. At about 10:24 a.m., 11 minutes after the call was received, officers engaged the suspect, he said.

"There were police cars that had been hit by gunfire. As officers were approaching the building, there was gunfire going off," Drake said.

"We feel, our response right now, from what I've seen, I don't have a particular problem with it. But we always want to get better. We always want to get there in two or three minutes," he said, adding that traffic was "locked down" at the time.

Traffic was indeed stopped along a nearby two-lane road with a turning lane as police tried to weave their way to the school.

Police have given unclear information on Hale's gender. For hours Monday, police identified the shooter as a woman. Later in the day, the police chief said Hale was transgender. After the news conference, Aaron declined to elaborate on how Hale identified.

In an email Tuesday, police spokesperson Kristin Mumford said Hale "was assigned female at birth. Hale did use male pronouns on a social media profile." Later Tuesday, at the news conference, Drake referred to Hale with female pronouns.

Authorities identified the dead children as Evelyn Dieckhaus, Hallie Scruggs and William Kinney. 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.

The Covenant School, founded as a ministry of Covenant Presbyterian Church, is in the affluent Green Hills neighborhood just south of downtown Nashville. The school has about 200 students from preschool through sixth grade, as well as roughly 50 staff members.

President Joe Biden said he had spoken to the police chief, mayor and senators in Tennessee. He pleaded with Congress to pass stronger gun safety laws, including a ban on "assault weapons."

"The Congress has to act," Biden said. "The majority of the American people think having assault weapons is bizarre, it's a crazy idea. They're against that."

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.