The deceased victims are believed to be students, officials say. A 15-year-old suspect who attends the school is in custody.

Authorities believe the shooter at Oxford High School in Michigan acted alone, Oakland County Undersheriff Michael McCabe said Tuesday.

They do not believe anyone else participated in planning the shooting, the sheriff’s official said.

McCabe noted the information is “pending further investigation” and added that law enforcement is currently interviewing students.

The shooting suspect, a 15-year-old sophomore, was not injured and there is no indication he was wearing body armor, McCabe said.

McCabe said authorities believe they know how the suspect was able to bring a handgun on to campus, but he declined to provide any details.

A Oakland County sheriff’s deputy, who is assigned to be on campus, “was one of the deputies that helped take him [the shooting suspect] into custody,” McCabe said. No shots were fired at the responding law enforcement officers during the shooting.

About 25 agencies and nearly 60 ambulances responded to the shooting on Tuesday, according to John Lyman, spokesperson for the Rochester Hills Fire Department.