Eight other people were wounded, some critically.

Oakland County Sheriff Michael Bouchard said investigators were still trying to determine a motive for Tuesday's shooting at Oxford High School in Oxford Township, a community of about 22,000 people roughly 30 miles (48 kilometers) north of Detroit.

"The person that’s got the most insight and the motive is not talking,” Bouchard said at a news conference late Tuesday night.

The suspect's father had bought the 9 mm Sig Sauer used in the shooting on Friday, Bouchard said, adding that he did not know why the man bought the gun. Bouchard said the suspect had practiced shooting with the gun and "posted pictures of the target and the weapon."

The three students who were killed were 16-year-old Tate Myre, 14-year-old Hana St. Juliana, and 17-year-old Madisyn Baldwin. Bouchard said Myre died in a patrol car as a deputy tried to get him to a hospital.

Bouchard said a teacher who received a graze wound to the shoulder was discharged from the hospital, but seven students ranging in age from 14 to 17 remained hospitalized with gunshot wounds, including a 14-year-old girl who was on a ventilator after surgery.

Bouchard said authorities were made aware of allegations circulating on social media that there had been threats of a shooting at the roughly 1,700-student school, but he said they didn’t know about the rumors until after the attack. He stressed how crucial it is for tips of the kind to be sent to authorities, while also cautioning against spreading social media rumors about the attack before a full investigation.

Authorities didn't immediately release the shooting suspect's name, but Bouchard said deputies arrested him within minutes of arriving at the school in response to a flood of 911 calls about the attack, which happened shortly before 1 p.m. He said the deputies arrested him after he emerged from a bathroom with the gun, which he said had seven rounds of ammunition still in it.

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