A 15-year-old sophomore opened fire at his Oakland County, Michigan, high school Tuesday, killing three students and injuring eight other people, police said.

The suspect, whose name has not been disclosed, was a sophomore at Oxford High School in southeast Michigan and had attended class before the shooting, the Washington Post reported, citing Oakland County Undersheriff Mike McCabe. 

The teenage boy is on suicide watch and is refusing to talk to authorities, leaving his motives unclear, McCabe said Tuesday night.

Authorities identified the students who were killed as Hana St. Juliana, 14, Madisyn Baldwin, 17, and Tate Myre, 16. Myre died in the car of an Oakland County Sheriff's Office deputy while on the way to the hospital, police said.

McCabe said the suspect fired around 15 to 20 shots before deputies confronted him and took him into custody, CNN reported. The teen shooter, an Oxford resident, did not resist arrest, police said.

The arrest happened within five minutes of dispatchers receiving the first of more than 100 911 calls regarding the incident, a report by Detroit Free Press said.

Eight more people, including a 47-year-old female teacher, were injured and transported to three nearby hospitals. Two of the injured underwent surgery, and the remaining six were in stable condition with various gunshot wounds, according to McCabe.

Authorities have recovered the weapon used in the incident — a Sig Sauer SP2022 9mm handgun — as well as several shell casings. The pistol contained seven rounds when it was confiscated, Oakland County Sheriff Michael Bouchard said.

Authorities said that the firearm was purchased by the shooter's father Friday, according to the Associated Press.

Officials were aware of how the teen shooter got the gun, but no additional information was disclosed, Detroit Free Press reported.

An investigation into the incident is currently being conducted by Oakland County police. No motive has been established for the fatal shooting, which police believe the gunman planned and did alone.

The Oakland County Prosecutor's Office has "begun the process of receiving information regarding the investigation" and "will issue appropriate charges quickly," county prosecutor Karen D. McDonald said.

Michigan Attorney General Dana Nessel, for her part, said her department has offered assistance to local law enforcement following the shooting.

"We must act to properly address gun violence in our schools and the ongoing threat of another unconscionable tragedy if we continue to only offer thoughts and prayers. Our kids deserve better," Nessel said.

President Joe Biden addressed the shooting after touring the Dakota Technical College in Minnesota.

"[M]y heart goes out to the families that are enduring the unimaginable grief of losing a loved one. You've got to know that that whole community is just in a state of shock right now," he said.

The teen shooter is being held at the Oakland County Children's Village, a juvenile center in Pontiac, Michigan. It is unclear what charges he faces over the shooting.

handgun-231696_1920 Representation. The gun used in a school shooting in Michigan Tuesday was bought by the shooter's dad four days before the incident, police said. Photo: Pixabay