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OXFORD TOWNSHIP, Mich. — A 17-year-old boy has become the fourth student to die from a school shooting in Michigan on Tuesday, authorities said Wednesday.

The Oakland County sheriff’s office identified the teen as Justin Shilling. Seven other people were wounded, some critically, including a 14-year-old girl who was placed on a ventilator after surgery.

Oakland County Sheriff Michael Bouchard said late Tuesday that investigators were still trying to determine a motive for the shooting at Oxford High School in Oxford Township, a community of about 22,000 people roughly 30 miles north of Detroit. A 15-year-old sophomore was taken into custody.

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

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 other 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.