Rearrested in the 1950 rising and pardoned in 1953, Albizu Campos was seized again within months of the 1954 Capitol attack and returned to La Princesa. In prison his health collapsed amid burns and lesions he attributed to radiation experimentation — claims officials dismissed as insanity but which supporters, and later researchers pointing to the era's documented federal radiation experiments on unwitting subjects, took seriously. He suffered a stroke in 1956 and spent his remaining years paralyzed and mostly speechless in custody or hospital confinement.
Pardoned by Governor Muñoz Marín only in November 1964, Albizu died on April 21, 1965; some 75,000 people followed his coffin to Old San Juan's cemetery. He had spent roughly twenty-six of his last twenty-nine years imprisoned, and his case — with the carpetas surveillance of a hundred thousand islanders — remains the foundation of the Puerto Rican political-prisoner tradition carried on by the FALN and Macheteros generations.