17 February 1937,
An enemy missile carried from the front as a war trophy exploded by surprise at the headquarters of the Union of Communist and Socialist Youth JSU in Bilbao. In the middle of the 36th war, at 17:00 a.m. the Executive Board met at Arenal No. 3. In the accident the Basque Agustín Zapirain and the delegates of Madrid Trifón Medrano and Rodríguez Cuesta died.
Source:
Miguel Usabiaga, Donostia rebelde. (Ed. Irreverent).