During celebrations to mark the Gudari Eguna (Day of the Basque Soldier), there was often rioting on the streets of San Sebastian. The police had therefore increased its presence in the area. On the afternoon of 27 September 1987, members of the National Police were heading towards the Paseo de la República Argentina. The convoy, consisted of two vans, containing a total of ten police officers.
ETA had previously planted a car bomb containing twenty kilos of ammonia and fifty kilos of nuts and bolts, which they detonated remotely as the first van passed. Wenceslao Maya Vázquez was driving the vehicle and died from severe skull injuries.
Four other police officers were seriously injured: Manuel Ibáñez, Isidro Gallego, Manuel Marurri and Miguel Ángel Rodríguez. Another 18 people were injured to differing degrees.