They were among about 100 students who headed out on the evening of Sept. 26, 2014, with a plan to steal some buses. This was a tradition that students at the school had done for many years: They would take the buses, use them to transport their peers to an event and then return them when they were done. The bus companies and the authorities mostly tolerated it.

The plan for the outing that evening was to secure several buses to carry students to a march in Mexico City several days later to commemorate a student massacre that had occurred in 1968.

Riding in two buses they had commandeered on earlier occasions, they stationed themselves on a main road on the outskirts of Iguala, planning to intercept a few buses.

“All of us were happy, having a blast, relaxed, happy with the drivers, playing,” a student later testified, according to the panel’s first report. It relied on testimony from survivors, government security officials and other witnesses as well as reports from an interagency government command center.

But the region’s security forces were already onto the students’ plans. The federal police stepped up patrols near the buses, and the command center linking local, state and federal police forces, as well as the military, kept tabs on the students.

At 8:15 p.m., the students made their first strike, boarding a bus that had stopped in front of a restaurant. The driver knew the drill; bus companies generally instruct drivers that in the event of a student hijacking, they should remain with the buses to ensure their safe return.