Authorities said a 15-year-old sophomore opened fire at his Michigan high school, killing three pupils, including a 16-year-old kid who died in the police car of a deputy on his way to the hospital.

Eight additional people were injured, including a 14-year-old girl who was placed on a ventilator following surgery.

The motive for Tuesday's shooting at Oxford High School, which is located in a village of around 22,000 people about 48 kilometers north of Detroit, Oakland County Sheriff Michael Bouchard said.

"The person with the most insight and motivation is not speaking," he stated late Tuesday during a news conference.

Deputies arrived at the school about lunchtime after 911 dispatchers received over 100 calls reporting a shooter.

Within minutes after their arrival, they arrested the student in a hallway. As deputies approached, he raised his hands in the air, Bouchard said.

Bouchard said the boy's father purchased the 9mm Sig Sauer used in the incident on Friday.

He had no idea why the man purchased the rifle, which his son had been photographing and practicing with, Bouchard added.

Authorities did not immediately release the boy's name.

Tate Myre, 16, Hana St. Juliana, 14, and Madisyn Baldwin, 17, were killed.

According to Bouchard, Myre died in a patrol car while a deputy attempted to transport him to an emergency room.

A teacher who sustained a graze wound to the shoulder has been released from the hospital, while seven students aged 14 to 17 stayed in the hospital overnight with gunshot wounds, he added.

When the child surrendered, the gun he was carrying contained seven further rounds of ammunition, Bouchard said.

According to Undersheriff Mike McCabe, the student's parents instructed him not to speak with investigators.

Police must obtain authorization to meet with a juvenile's parents or guardian, he noted.

Prosecutor Karen McDonald of Oakland County said in a statement that her office expected to file charges swiftly and that an update would be provided Wednesday.

Authorities were made aware of social media posts alleging threats of a shooting at the about 1,700-student school, but Bouchard said they were unaware of the allegations until after the attack.

He emphasized the critical nature of reporting such tips to police while also cautioning against spreading social media rumors before conducting a comprehensive investigation.

McCabe also downplayed the significance of an incident in early November in which a deer head was thrown from the school roof, which he claimed had nothing to do with the shooting.

Following the vandalism, school authorities posted two messages to parents on the school's website, stating that they were reacting to rumors of a threat against the school but had discovered none.

Bouchard stated that the pupil was not previously involved with his department and that he was unaware of any disciplinary history at the school.

"That is part of our investigation into what occurred prior to this event and, if any signs were missed, how and why were they missed," he explained.

During the attack, the university was placed on lockdown, with some youngsters taking refuge in sealed classrooms.

They were eventually escorted to a nearby Meijer grocery shop so their parents could pick them up.

The district announced in a statement that it would close all of its schools for the remainder of the week.

Isabel Flores, 15, a ninth-grade student, told WJBK-TV that she and other classmates heard gunshots and witnessed another kid bleeding from the face.

They immediately fled the area through the school's rear, she explained.

Authorities stated that they were combing through the suspect's smartphone, school camera footage, and social media posts for any indication of probable motivation.

In November, school authorities released two messages to parents on the school's website, claiming to be responding to rumors of a threat against the school in the aftermath of an odd vandalism incident.

According to a November 4 letter from Principal Steve Wolf, someone dropped a deer head into a courtyard from the school's roof, painted numerous windows on the roof with red acrylic paint, and painted concrete near the school building with the same paint during the early morning hours.

Without mentioning that incident specifically, a subsequent article on November 12 informed readers that "there has been no threat to our building or our students."

The sheriff and undersheriff both stated emphatically that Tuesday's shooting had nothing to do with the deer head or any previous inquiry conducted by their office.

"That was a distinct incident involving a distinct student," McCabe stated.

Robin Redding, a concerned parent, stated that her son, Treshan Bryant, is a 12th-grader at the school but was absent Tuesday.

Redding stated that her kid had overheard threats of a shooting.

"This cannot be coincidental," she stated.

Bryant stated that he texted numerous younger cousins in the morning, and they expressed disinterest in attending school, giving him a horrible vibe.

He requested permission from his mother to complete his tasks online.

Bryant stated that he had been hearing vague warnings regarding a shooting "for a long time now."

Leeann Dersa held back tears as she hugged friends and neighbors at a vigil Tuesday night at LakePoint Community Church. Dersa has spent practically her whole 73-year life in Oxford.

Her grandchildren were high school students.

"Scared the living daylights out of us all. Dersa described the shooting as "heinous."

Pastor Jesse Holt said word of the massacre came into him and his wife, including texts from some of the congregation's 20 to 25 youngsters.

"Some were terrified, cowering beneath their desks and texting us to say, 'We're safe, we're fine.' We heard gunfire but are unharmed.' They were attempting to calm us, or so it felt," he explained.