Complex sentence: In 1933-4 this was modernized and became the Alcatraz Federal Penitentiary, the most notorious Alcatraz prison which housed some of America's most dangerous crooks between 1934 and 1963.
Split into simpler sentences: In 1933-4, this was modernized and became the Alcatraz Federal Penitentiary. It housed some of America's most dangerous criminals between 1934 and 1963.