Al Capone Mabel Walker Willebrandt recognized that mob figures publicly led lavish lifestyles yet never filed tax returns, and thus could be convicted of tax evasion without requiring hard evidence to get testimony about their other crimes. She tested this approach by prosecuting a South Carolina bootlegger. In 1927, the Supreme Court ruled in "United States v. Sullivan" that illegally earned income was subject to income tax; Justice Oliver Wendell Holmes Jr. rejected the argument that the Fifth Amendment protected criminals from reporting illegal income. The IRS special investigation unit chose Frank J. Wilson to investigate Capone, with the focus on his
Frank Capone with mobster John Torrio. By 1918, Torrio had moved to Chicago to help a relative defend his rackets, and Torrio soon asked Al and later Frank to join him there. By 1920, Torrio had taken charge of the South Side Gang and the Prohibition era had started. As the gang increased in power and wealth, so did Al and Frank. In 1923, Chicago voters elected a new mayor, William Dever, who proceeded to crack down on Torrio, the Capone brothers, and their South Side Gang. In response, Torrio tasked Al with creating speakeasies, brothels, and illegal gambling dens in Cicero,