Mario Lacruz Muntadas (Barcelona 1929-2000) wrote in 1953 El inocente, a novel in the existentialist tradition. Since it was written as a detective story it is regarded as the forerunner of the Spanish crime fiction. It was published by Editorial Caralt and translated into eight languages (among them an English edition entitled The Suspect). In 1955 won the Simenon Award.
If interested you can find additional information here (in English).
Francisco Ortiz in his blog Novela negra y cine negro has written about this book (in Spanish):