On the morning of 11 December 1987, the Argala unit of ETA militar parked a car containing 250 kilograms ammonal at a side entrance to the Guardia Civil Barracks on Avenida Cataluña in Zaragoza. At 6.10 am, terrorist Henri Parot alighted from the stolen vehicle, activated the detonator by remote control and fled the scene.
The officers on duty in the security hut suspected that it was an attack. One of them chased after the ETA member, who got into a wating getaway car. The other went up to the apartments to warn an explosives expert but did not get there in time. The bomb exploded in the block, inhabited by some 40 families of civil guards and children of officers from other parts of Spain who were studying to enter the academy.
The building collapsed and the explosion left a hole measuring over 10 metres in the wall. The blast also damaged nearby homes. Eleven people, including six minors, were killed instantly and a further 88 were injured.
In the confusion of ambulances and security vehicles coming and going, a military minibus taking soldiers to the hospital to donate blood failed to stop at a traffic light. It struck and killed Tomás Lafontana Giménez, who was driving his moped. Although Lafontana was not directly killed in the explosion, the attack had created such chaos in the area that the Ministry of the Interior also classified him as a victim of terrorism.