Virgilio Mas Navarro and his colleague Juan Antonio Querol Queralt were leaving the Bruc barracks in Barcelona at around 1.30 pm by car to go to Sants station, when they were shot by ETA members José Luis Urrusolo Sistiaga and Fernando Díez Torres. In all, 34 rounds were fired from a sub-machine gun and a pistol, killing the two NCOs instantly. Mas Navarro was taking Querol Queralt to Sants station to take a train to Puig (Valencia), where his wife and son were living. Mas Navarro had been living in Barcelona for five years after passing the civil service exams required to join the band of the Military Government of Barcelona, where he played the euphonium and trombone.
At the time of the dual murder, the streets were very crowded, particularly with students from the nearby Polytechnic University of Barcelona. Numerous eyewitnesses told the media that the two ETA members had been waiting for about ten minutes for the officers to pass. After firing on the two NCOs, they escaped in a car that been stolen some days earlier.