The students at Oxford High School were trudging between rooms during passing time, the short recess between classes. It was late November 2021, a mid-day like any other. Oxford is located just outside Detroit, Michigan, so it was cold, about minus 1C, and snow covered the ground. At 12.46pm, 15-year-old Ethan Crumbley ambled to the south end of one of the school’s hallways.

Ethan, wearing a grey hoodie, jeans and a backpack, moved easily among the other students. He was lanky, with hunched shoulders. Squinting through his glasses, dark hair falling messily in front of his eyes, he looked somewhat like a ruffled hatchling. He was a quiet boy, an average student and, according to some of the staff at Oxford High School, no trouble at all.

Ethan entered a bathroom around 12.50pm, walked into one of the stalls and put down his pack. He took out a black notebook, pens, a juice bottle and his laptop. At the bottom of the bag, a jet-black Sig Sauer 9mm handgun jostled among rounds of ammunition. As Ethan fed the gun chamber with bullets, several other kids heard the rhythmic sound of metal on metal, like the tick of a grandfather clock. Then, click-clack, the sound of the gun cocking.