Officials are working to determine the motive behind a deadly shooting at a Christian school in Nashville as more details emerge about the shooter who killed three students and three staff members Monday.

The shooter was identified by police as 28-year-old former student Audrey Elizabeth Hale. Hale shot open a glass side door and entered the Covenant School with three weapons, including an AR-style rifle, an AR-style pistol and a handgun, according to police.

Officers killed the shooter in a common area on the second floor of the school, according to a statement from police. Metropolitan Nashville Police Chief John Drake said at a press conference Tuesday the shooter bought seven firearms legally from five local gun stores, including the three used in the attack. Police said previously officers found a sawed-off shotgun and a second shotgun at the shooter’s home.

Drake said the shooter’s parents believed their child had only one gun and sold it, but the suspect had been hiding several weapons in the house. Drake said if it had been reported that the shooter was suicidal or homicidal, police would have tried to take the weapons, “but as it stands we had absolutely no idea actually who this person was.”

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Who was the Nashville school shooter?

Drake said Tuesday that police interviewed the shooter’s parents, who said the shooter was “under doctor’s care for an emotional disorder.” Police said the shooter was a former student at the small, private Christian school who had no criminal history.

Bill Campbell, a headmaster of the Covenant School from 2004 to 2008, told NBC he could not recall any issues the shooter might have had as a third grader at the school in 2005 and a fourth grader in 2006. The Covenant School was founded in 2001 as a ministry of Covenant Presbyterian Church, according to the school’s website.