The Oxford High School shooting suspect, identified on Wednesday as 15-year-old Ethan Crumbley, made a video the night before the attack discussing how he would go about killing fellow students, according to The Associated Press.
Crumbley is accused of killing four students and injuring seven others on Tuesday, Oakland County Sheriff's Lt. Tim Willis said.
Oakland County authorities offered no motive a day after the violence at the school, roughly 30 miles north of Detroit.
The four students killed were identified as 16-year-old Tate Myre, 14-year-old Hana St. Juliana, 17-year-old Madisyn Baldwin and 17-year-old Justin Shilling.
On Wednesday, authorities charged Crumbley as an adult with murder, attempted murder, terrorism causing death, and gun crimes. Defense attorney Scott Kozak entered a plea of not guilty on Crumbley's behalf.
In court, assistant prosecutor Marc Keast said that Crumbley entered a restroom with a backpack and came out holding a semiautomatic handgun, firing at students while moving down the hallway.
Prosecutor Karen McDonald said the shooting was premeditated, based on a ''mountain of digital evidence'' collected by police, per The Hill.
''This was not just an impulsive act,'' McDonald said. ''We send our kids to school. We think that they're going to be safe, so the only thing that I can do as the prosecutor is ensure that I will do everything I can to prosecute this case and pursue justice for these victims but also to speak out and say that we need better gun laws.''
Judge Nancy Carniak ordered the transfer of Crumbley from a juvenile facility to county jail on Wednesday. He will be held without bail.