The shooter who killed six people at a school in Nashville, Tennessee, on Monday bought seven guns legally and hid them at home, police say.
Investigators say the suspect's parents felt the 28-year-old should not own weapons, and did not realise the guns had been concealed in their house.
Six people, including three children age nine, were killed in the attack at the Covenant School.
The suspect was under "doctor's care for an emotional disorder", police say.
And it was the school that was targeted rather than any particular individual, officers revealed.
Tennessee has no laws that allow police to seize guns from violent suspects.
Despite the absence of such so-called red-flag laws, police said they would still have sought to have the weapons confiscated if authorities had had any warning that the suspect could have posed a threat.
The pupils killed in the attack were Evelyn Dieckhaus, Hallie Scruggs and William Kinney.
Three adult employees at the privately run Christian school also died: Cynthia Peak, 61, Katherine Koonce, 60, and Mike Hill, 61.
Police have spoken to the parents of the suspect, 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 guns, including a semi-automatic rifle.
The attack took place after the killer conducted surveillance of the premises, drew maps and wrote what police described as a "manifesto".
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