On May 30, 1897, Angiolillo, among at least ten thousand other people, attended a demonstration in Trafalgar Square against the brutal repression of worker's rights movements within Spain, specifically under Cánovas.

Organized by the Spanish Atrocities Committee led by the anarchist Joseph Perry, a wide range of activists spoke to the crowd, including Fernando Tarrida del Mármol and Charles Malato.

The German anarchist Rudolf Rocker, who was also present, wrote the following about the meeting: "That night when Gana showed us his crippled limbs, and the scars over his entire body left by the tortures, we understood that it is one thing to read about such matters, but quite another to hear about them from the very lips of the victims" ... "We all sat there as if turned to stone, and it was some minutes before we could utter a few words of indignation.

"[5]Under a false identity of a reporter for the Il Popolo newspaper by the name of Emilio Rinaldini, Michele Angiolillo traveled to Spain from London, passing through Paris and Bordeaux.

[6] When he reached Madrid, he learned that Cánovas had traveled to the thermal bath resort of Santa Águeda (now a psychiatric hospital) in Mondragón, Guipúzcoa, and decided to pursue him there.

[8]There is some evidence that he originally planned to kill one or two young members of the Spanish royal family, but was dissuaded by Puerto Rican nationalist leader Ramón Emeterio Betances, who suggested Cánovas del Castillo as a target instead.