Liborio Arana Gómez was murdered in the multiple killing at the Aldana de Alonsotegui bar. A powerful bomb went off, consisting of five or six kilos of Goma-2 with an electric detonation system, triggered accidentally by Liborio Arana when he moved the device.
As well as Liborio, three other people were killed: Pacífico Fica Zuloaga, María Paz Armiño and Manuel Santacoloma Velasco. The attack was carried out by the Grupos Armados Españoles (Spanish Armed Groups). The bar was frequented by sympathisers of the Basque Nationalist Party and other left-wing nationalist groups.