OXFORD TOWNSHIP, Mich. (AP) — A 15-year-old sophomore opened fire at his Michigan high school on Tuesday, killing three students and wounding six other people, including a teacher, authorities said.

Oakland County Undersheriff Mike McCabe said at a news conference that he didn't know what the assailant's motives were for the attack at Oxford High School in Oxford Township, a community of about 22,000 people roughly 30 miles (48 kilometers) north of Detroit.

Officers responded at around 12:55 p.m. to a flood of 911 calls about an active shooter at the school, McCabe said. Authorities arrested the suspect at the school and recovered a semi-automatic handgun and several clips.

“Deputies confronted him, he had the weapon on him, they took him into custody,” McCabe said, adding that the suspect wasn't hurt when he was taken into custody and he refused to say how he got the gun into the school.

Authorities didn’t immediately release the names of the suspect or victims.

Tim Throne, the superintendent of Oxford Community Schools, said he didn't yet know the victims' names or whether their families had been contacted.

“I’m shocked. It’s devastating,” the shaken superintendent told reporters.

The school was placed on lockdown after the attack, with some children sheltering in locked classrooms while officers searched the premises. They were later taken to a nearby Meijer grocery store to be picked up by their parents.

McCabe said investigators would be looking through social media posts for any evidence of a possible motive.

Robin Redding, the parent of a 12th-grader, told The Associated Press that there had been rumblings of trouble at the school.

“He was not in school today. He just said that ‘Ma I don’t feel comfortable. None of the kids that we go to school with are going today,’” Redding said.