OXFORD TOWNSHIP, Mich. (AP) - A 15-year-old sophomore opened fire at his Michigan high school, killing three students, including a 16-year-old boy who died in a deputy’s patrol car on the way to a hospital, authorities said.

Eight other people were wounded, some critically, including a 14-year-old girl who was placed on a ventilator after surgery. Investigators were still trying to determine a motive for the shooting Tuesday at Oxford High School, located in a community of about 22,000 people roughly 30 miles north of Detroit, Oakland County Sheriff Michael Bouchard said.

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

Deputies rushed to the school around lunch time as more than 100 calls flooded 911 dispatchers with reports of a shooter.

They arrested the student in a hallway within minutes of their arrival. He put his hands in the air as deputies approached, Bouchard said.

The boy’s father on Friday bought the 9 mm Sig Sauer used in the shooting, Bouchard said. He didn’t know why the man bought the gun, which his son had been posting pictures of and practicing shooting, Bouchard said.

Authorities didn’t immediately release the boy’s name.

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 an emergency room.

A teacher who received a graze wound to the shoulder has left the hospital, but seven students ranging in age from 14 to 17 remained hospitalized through the night with gunshot wounds, he said.

The gun the boy was carrying had seven more rounds of ammo in it when he surrendered, Bouchard said.

Undersheriff Mike McCabe said the student’s parents advised their son not to talk to investigators. Police must seek permission from a juvenile’s parents or guardian to speak with them, he added.

Oakland County Prosecutor Karen McDonald said in a statement her office expects to issue charges quickly and that an update would be given Wednesday.

Authorities were made aware of posts on social media that said there had been threats of a shooting at the roughly 1,700-student school, but Bouchard 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 before a full investigation.