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OXFORD TOWNSHIP, Mich. (AP) — Authorities say a 17-year-old boy has become the fourth student to die from a school shooting in Michigan.

The Oakland County sheriff’s office identified the teen Wednesday as Justin Shilling.

The three other students who were killed were 16-year-old Tate Myre, 14-year-old Hana St. Juliana, and 17-year-old Madisyn Baldwin.

Myre died in a patrol car as a deputy tried to get him to an emergency room.

A 15-year-old sophomore opened fire Tuesday at Oxford High School in Oakland County, Michigan. The suspect remains in custody.

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

Seven 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 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 semi-automatic handgun, which his son had been posting pictures of and practicing shooting, Bouchard said.

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.

Bouchard said the student in custody had no previous run-ins with his department and he wasn’t aware of any disciplinary history at school.

“That’s part of our investigation to determine what happened prior to this event and if some signs were missed how were they missed and why,” he said.

Authorities said they were searching the suspect’s cellphone, school video footage and social media posts for any evidence of a possible motive.

The district said in a statement that all of its schools would be closed for the rest of the week.