Guillermo Senent Pallarola was 23 years old and had just got his first job working as an industrial electronics technician for Alstom. Although he did not normally start work that early, on 11 March, 2004 the employees had been called in for a routine medical check-up. Guillermo boarded the train in Guadalajara, where he lived, and travelled into Madrid with his friend David Santamaría. They were both killed at El Pozo station.
11 March 2004 fell on a Thursday. Early that morning, a number of terrorists with links to Al-Qaeda planted thirteen bombs on four suburban trains covering routes running through Madrid. Ten of the bombs exploded between 7.37 and 7.39 am, when the trains were at Atocha, El Pozo and Santa Eugenia stations and alongside Calle Téllez. 191 people were killed in the attack and around 1,500 were wounded. It was the deadliest terrorist attack in Spanish history. On 3 April 2004, agents from the Special Operations Group (GEO) were about to enter an apartment in Leganés where the perpetrators of the attacks were believed to be hiding when the terrorists detonated twenty kilograms of explosives in an act of collective suicide. The ensuing blast killed one of the officers, bringing the total number of people killed by the 11 March bombers to 192.