The Spanish police thwart an attempt by ETA to detonate 50 kg of explosives at 3:55 p.m. inside Madrid's busy Chamartín Station.

ETA, an acronym for Euskadi Ta Askatasuna, was an armed Basque nationalist and far-left separatist organization in the Basque Country between 1959 and 2018. The group was founded in 1959 during the era of Francoist Spain, and later evolved from a pacifist group promoting traditional Basque culture to a violent paramilitary group. It engaged in a campaign of bombings, assassinations, and kidnappings throughout Spain and especially the Southern Basque Country against the regime, which was highly centralised and hostile to the expression of non-Castilian minority identities. ETA was the main group within the Basque National Liberation Movement and was the most important Basque participant in the Basque conflict.

An explosive is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material, which may either be composed solely of one ingredient or be a mixture containing at least two substances.

Madrid is the capital and most populous municipality of Spain. It has almost 3.5 million inhabitants and a metropolitan area population of approximately 7 million. It is the second-largest city in the European Union (EU), second only to Berlin, Germany, and its metropolitan area is the second-largest in the EU. The municipality covers 604.3 km² (233.3 sq mi) geographical area. Madrid lies on the River Manzanares in the central part of the Iberian Peninsula at about 650 m (2,130 ft) above mean sea level. The capital city of both Spain and the surrounding autonomous community of Madrid, it is also the political, economic, and cultural centre of the country.