Two former students kill the vice-principal of Secondary School No. 13 in Torreón

Two 18-year-old brothers, both former students, attacked staff at Secondary School No. 13 in the La Unión neighbourhood of Torreón on Thursday morning. The vice-principal was killed. State prosecutor Federico Fernández Montañez said both suspects were detained. Governor Manolo Jiménez Salinas said the devices used were fireworks, not firearms.

The attack began around 8.30 a.m. Local reports said the two men came in with machetes and crude explosive devices. Fernández told reporters that preliminary work showed two people had attacked administrative staff, and that the vice-principal, a woman, had died. He called it a brutal attack. Pupils sheltered in classrooms after the first blasts. Neighbours who heard the detonations entered the school, held the two men, and kept them until police arrived. Parents were later filmed striking the suspects. That second scene is on video. It is not the same event as the attack inside the building.

The injury count is not settled. Reuters reported three people injured besides the dead vice-principal. The governor later spoke of five wounded, among them two students and three teachers. Fernández then put the final toll at four wounded, two of them serious and two stable, plus the vice-principal dead. A one-person gap between the governor and the prosecutor, on the same afternoon, is the sort of revision that follows a hospital list rather than a crime-scene list. The dead woman's name had not been released in the first wire accounts.

Jiménez Salinas's weapon finding matters because the first local reports said machetes and rudimentary explosives. He said investigators were treating the blasts as rockets or petards and had ruled out guns. A petard in a school corridor can kill and can also be mistaken, in the first hour, for a grenade. The distinction decides the charge. An attack with a firearm pulls a different statute from an attack with a blade and a firework. Fernández has not yet said which charging path the state will use. He has said the two are former students of the same school, and that they are brothers.

School attacks of this kind are uncommon in Mexico, where the public violence that fills crime figures is usually tied to organised groups rather than to former pupils walking back through a gate at 8.30 a.m. Coahuila has had its share of the first kind. Thursday's case, on the prosecutor's account, is the second. The detentions were not a tactical operation. They were neighbours and parents in the courtyard. That fact will sit in the file next to whatever the two men say about why they came back.

Secondary School No. 13 is a general secondary in La Unión, a working neighbourhood of Torreón, a city of the Laguna region on the Coahuila side of the border with Durango. The school day had already started. The vice-principal was on duty. Those two facts are why the dead and the wounded are staff and students rather than passers-by.

What Friday needs from the state is a single injury list, the vice-principal's name, and a charge that matches the weapon the governor has already described. Until then the public record is a dead administrator, two brothers aged 18 in custody, and a dispute of one or two over the number of wounded.