Al Capone ultimately went down for not paying his taxes on the income that he accrued throughout the 1920s. The man who proved that Capone needed to pay up was Frank Wilson, an accountant who worked for the federal government.
Capone was often involved in violent criminal activity but the government could not produce a solid case against him so his crimes. Capone also made about $60,000,000 a year and the government had no record that he paid the government.
Frank Wilson sent consistent updates to his superiors within the government. In a March 1931 letter, Wilson alerts the Treasury Department that he found proof of more unreported income:
“The Capone investigation is going steadily ahead. Not as fast as I would like to have it, but the evidence in the case against Al has been strengthened since my last letter to you.
I sent you a copy of an affidavit made by the Reverend H. C. Hoover, by which we established through admissions made by Al Capone to him that he (Capone) was the owner of the gambling establishment of which we have the book records reflecting a net profit of $574,000, during a period of twenty-four months. I am enclosing a copy of a statement made by Chester Bragg, prominent real estate dealer in Cicero, in which he states that Al Capone admitted to him that he was the owner of this establishment.”
While Elliot Ness had a role in busting the breweries and distributors in Chicago, accountants and undercover agents like Frank Wilson were the ones actively pursuing Capone and formulating a solid case against him.
 “Frank Wilson.”History. 23 April 2010. https://www.history.com/topics/us-government/frank-wilson.
 Wilson, Frank J.“Letter From Frank Wilson Updating the Capone Investigation.,1931.”Treasury Department. https://en.wikisource.org/wiki/Letter_from_Frank_Wilson_updating_the_Capone_investigation,_March_27,_1931.