“Sacamantecas” turns on Spain’s first recorded serial killer, Juan Díaz de Garayo. 　　In two killing sprees over 1872-79, the ageing and illiterate farm laborer raped and murdered six women in Vitoria in Spain’s Basque country. The murders coincided with Spain’s bloody Third Carlist War. “Sacamantecas” looks set to explore not only has figure but also context.