Tuesday, Oakland County Sheriff Michael Bouchard said, noting that more than a hundred 911 calls were placed.

That, I believe, interrupted what potentially could have been seven more victims," Bouchard said at a news conference Tuesday night.

A deputy with the Oakland County Sheriff's Office is assigned to the school and that deputy helped take the suspect into custody, Oakland County Undersheriff Michael McCabe said.

Most were treated and released at a staging area, he said.

What we know about the suspect

The suspect, a sophomore at the school, is being held at Oakland County Children's Village -- a juvenile detention facility -- and is on suicide watch where he is being checked on every 15 minutes, said David Coulter, the Oakland County executive.

"We don't have a motive at this point in time," McCabe said Tuesday.

The semiautomatic handgun recovered by law enforcement was bought by the suspect's father on Friday, Bouchard said.

What we know about the investigation

Processing of the scene at the high school was expected to stretch into the overnight hours and investigators have a "tremendous amount of video footage" to review from cameras in the school, Bouchard said.

Two 15-round magazines were found at the scene, Bouchard said, noting at least 12 rounds were fired.

A search warrant was executed at the suspect's home Tuesday, McCabe said.