He hid the weapons at his parents' home, but the motives behind the attack on the Nashville school are unclear
The gunman who killed six people at a Nashville, Tennessee school on Monday bought seven guns legally and hid them at home, police say.
Six people, including three nine-year-old children, were killed in the attack on the Christian school.
The author was under the "doctor's care for an emotional disorder", say the police.
The students killed in the attack were Evelyn Dieckhaus, Hallie Scruggs and William Kinney.
Three employees at the Christian school also died: Cynthia Peak, 61, Katherine Koonce, 60, and Mike Hill, 61.
Police have spoken to the parents of Audrey Hale, who was killed by police less than 15 minutes after the attack began.
Hale, who identified as transgender and was a former student at the school, was armed with three weapons, including a semi-automatic rifle.
Before the attack she had created several maps.
A police spokesman said the attacker was not targeting anyone in particular, but was targeting "this school, this building".