A 15-year-old student opened fire at his Michigan high school on Tuesday, killing three students, including a 16-year-old boy who died in a police car on the way to hospital.
A 17-year-old girl and a 14-year-old girl were also killed in the attack at Oxford High School in Oxford Township, a community of about 22,000 people 30 miles (48km) north of Detroit.
Eight others, including a teacher, were injured. Several of them remain in critical condition, including a 14-year-old on a ventilator.
The 15-year-old is in custody after being arrested at the school, although his motive remains unclear, according to Oakland County Undersheriff Mike McCabe.
Officers responded at around 12:55 pm local time to a flood of 911 calls about an active shooter.
The suspect was believed to have acted alone and was arrested without resistance after firing 15 to 20 shots.
“The whole thing lasted five minutes,” Mr McCabe said.
Authorities said they recovered ammunition and a semi-automatic handgun, found to have been bought by the suspect’s dad on 26 November.
Oakland County Sheriff Michael Bouchard said that the suspect had practised shooting with the 9mm Sig Sauer and posted pictures of it and the target online.
It is unknown why the boy’s father bought the gun.
Tim Throne, the superintendent of Oxford Community Schools, said: “I’m shocked. It’s devastating.”
The school was placed on lockdown after the attack, with some children sheltering in locked classrooms while officers searched the premises.
They were later taken to a nearby shop to be picked up by their parents.
Michigan Governor Gretchen Whitmer called the shooting “horrific.”
“As Michiganders, we have a responsibility to do everything we can to protect each other from gun violence,” she said.