Michigan prosecutors on Wednesday charged the suspect in this year's deadliest school shooting with murder and other charges as investigators sought to determine what prompted the spree that killed four students and wounded seven other people.
The alleged shooter, Ethan Crumbley, a 15-year-old sophomore at a high school in Oxford, Michigan, about 40 miles (65 km) north of Detroit, was charged with a slew of criminal counts, Oakland County Prosecuting Attorney Karen McDonald said.
“I am absolutely sure after reviewing evidence that it isn’t even a close call," she said at a briefing. "It was absolutely premeditated.”
Crumbley, who is being charged as an adult, faces 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, she said.
"It's possible there could be more additional charges issued very soon," McDonald said.
The suspect opened fire on Tuesday at Oxford High School with a handgun his father had purchased four days earlier, authorities said.
Three of the students -- Tate Myre, 16, Hanna St. Julian, 14, and Madisyn Baldwin, 17, -- died on Tuesday, while the fourth, 17-year-old Justin Shilling, died on Wednesday, the Oakland County Sheriff's Office said.
A teacher and six other students were wounded, some of whom remain in critical condition, authorities said.
The shooting spree was the deadliest on US school property this year, according to Education Week. It was the latest in a decades-long string of deadly American school shootings that will likely fuel debates about gun control and mental health care.
More than 50,000 people had signed an online petition as of Wednesday morning to rename the school's stadium after Myre, who was a member of Oxford High's football team, saying he tried to disarm the shooter.
"Tate is not just a hero to his fellow students at Oxford High School but a legend, his act of bravery should be remembered forever and passed down through generations," the petition on Change.org said.
Oakland County Sheriff Michael Bouchard said in an interview on CNN earlier on Wednesday that it was clear that the shooter intended to kill people.
"He was shooting people at close range, oftentimes towards the head and chest. ... It's just absolutely coldhearted murders," he said, adding that the shooter fired at least 30 shots.
Bouchard said investigators were poring over writings of the shooter they obtained in the middle of the night that contain "some of his thoughts." They were also watching surveillance videos of the incident.
"We can't get the motive from the suspect that we have in custody, but we think we've got a path to get a lot of supportive information as to how and why this occurred," he said.
The suspect was disarmed and taken into custody by sheriff's deputies minutes after the shooting began. He declined to speak with investigators after his parents retained a lawyer and denied authorities permission to interview their son, Bouchard said.
Bouchard credited swift action by his deputies for preventing greater loss of life, saying they arrived on the scene within minutes and moved straight toward the sound of gunshots.
Officers confronted the young assailant advancing down a hallway toward them with a loaded weapon, and he put his hands over his head and surrendered, Bouchard said.