The 15-year-old was identified by officials as Ethan Crumbley, a student at Oxford High School, where the shootings took place.
He was charged with one count of terrorism causing death, four counts of first-degree murder, seven counts of assault with intent to murder, and 12 counts of possession of a firearm in the commission of a felony.
Three students died after being struck and a fourth perished Wednesday as a result of his injuries.
Oakland County Prosecutor Karen McDonald said her team is confident that they can prove that Ethan planned the attack, citing “a mountain of digital evidence,” including videos and social media posts.
She declined to answer whether the shootings appeared to be targeted.
“We as prosecutors are ethically bound to not reveal any statements that could jeopardize the prosecution of the case and providing a fair trial. Because if that happened, that would be tragic for the families of the victims of these victims,” McDonald said.
In a separate gaggle, Oakland County Sheriff Michael Bouchard told reporters that he didn’t see any connection between the students who were shot and the shooter.
“And based on what I saw in the video, it appears to be random,” he said.
Preliminary evidence indicates Ethan shot people in a school hallway and nearby classrooms after emerging from a bathroom wielding a 9-millimeter Sig Sauer pistol.
Over a dozen casings were recovered. Some bullets were still in the gun when the boy was arrested.
The deceased were identified as Hana St. Juliana, 14; Tate Myre, 16; Madisyn Baldwin, 17; and Justin Shilling, 17.
Seven other students were in the hospital receiving care after being struck.
The accused shooter’s parents advised their son not to cooperate with authorities.
“We have no information on whether he was bullied or why he would do that. But I also would say there is nothing that would justify this. So the why is more, I think, us grasping at how could somebody do this, versus justification for doing it,” Bouchard said. “It’s a big difference. We can’t wrap our head around the incredible cold-blooded murder of kids. And so we look for a why there is no credible, reasonable why. This was an evil act. And it appears to be random.”