OXFORD TWP, Mich. — A 15-year-old boy was charged with murder and terrorism for a shooting that killed four fellow students and injured others at a Michigan high school, authorities said Wednesday, revealing that his parents were summoned just a few hours before the bloodshed.

No motive was offered by Oakland County authorities, a day after violence at Oxford High School, roughly 30 miles north of Detroit. But prosecutor Karen McDonald said the shooting was premeditated, based on a “mountain of digital evidence” collected by police.

“This was not just an impulsive act,” McDonald said.

Indeed, sheriff's Lt. Tim Willis told a judge that Ethan Crumbley recorded a video the night before the violence in which he discussed killing students.

Crumbley was charged as an adult with murder, attempted murder, terrorism causing death and gun crimes. During his arraignment, he replied, “Yes, I do,” when asked if he understood the charges.