 The early to mid-1960s saw the publication of the only two volumes of work put into print during Castillo's lifetime, "Poema Tecún Umán" and "Vámonos patria a caminar".In 1966, he clandestinely returned to Guatemala and joined the guerrilla struggle with the Rebel Armed Forces, where he served as the chief of propaganda and education.After operating in the Sierra de las Minas for several months, he was captured by government forces and taken to Zacapa barracks alongside his comrade, Nora Paíz Cárcamo in March 1967.