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 (48 km) north of Detroit, Oakland County Sheriff Michael Bouchard said.