(CNN) — School bells were replaced by police sirens Tuesday after a mass shooting at Oxford High School in Oxford, Michigan, left three students dead, officials said.

Seven additional students and a teacher were wounded by gunfire and a 15-year-old suspect is in custody.

Vigils were held Tuesday night as the community, located about 42 miles north of Detroit, processed the trauma of a deadly shooting that forced terrified students to barricade themselves into classrooms, unsure whether they would emerge unscathed.

Here’s what we know about the shooting:

How the incident unfolded

Deputies were dispatched to the school at 12:52 p.m. Tuesday, Oakland County Sheriff Michael Bouchard said, noting that more than a hundred 911 calls were placed.

As police were swarming the campus, students and staff began barricading doors and hiding in classrooms.

“The only information I had is he came out of a bathroom with the weapon and I don’t know where he went first,” Bouchard told reporters Tuesday, referring to the suspect.

Law enforcement officers quickly entered the building and had him in custody within three minutes of their arrival, the sheriff said.

Once the suspect encountered the officers, he put his hands up and they took a gun from him before placing him in custody.

The gun, a 9MM Sig Sauer SP2022 pistol, was loaded with seven rounds.

“He had a loaded firearm and he was coming down the hall. 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.

Investigators believe there were no other weapons involved and there’s no indication the suspect was wearing body armor.

No shots were fired by responding law enforcement and the suspect was not injured, McCabe said.

Around 25 agencies and close to 60 ambulances responded to the school Tuesday, according to John Lyman, public information officer for the Rochester Hills Fire Department.

What we know about the victims

Investigators identified the victims who died as Tate Myre, 16, Hanna St. Julian, 14, and Madisyn Baldwin, 17.

Myre died in a patrol car as a deputy was attempting to rush him to the hospital due to the “severity of his wounds,” Bouchard said.

Eight others — seven students and a teacher — were shot, Bouchard said. Three are in critical condition with gunshot wounds, including a 14-year-old girl who is on a ventilator after having surgery. A 14-year-old boy is in serious condition with a gunshot wound to the jaw and head, Bouchard said. Three students are in stable condition and the teacher who was shot has been discharged.

There were multiple other non-life-threatening injuries sustained by people as they were rushing out of the school, Bouchard 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. “We are still investigating that.”

The suspect’s parents hired an attorney and have not permitted him to talk with police, officials said.

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. Bouchard said authorities seized a phone and are examining other seized items.

Investigators are also looking into a social media post apparently made by the suspect that appeared to show the weapon and a target, Bouchard said. “We are going to do a deep dive on the social media and all the activities of this young man.”

Bouchard said his department was not aware of any prior concerns at the school.

McCabe said the suspect could be charged as an adult, but that is up to the Oakland County Prosecutor’s Office.

Prosecutor Karen D. McDonald said in a statement Tuesday her office has “begun the process of receiving information regarding the investigation” into the shooting.

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