Chicago gangster Al Capone was convicted of federal income tax evasion in 1931 in Chicago, Illinois, in a landmark case that demonstrated that financial records — rather than direct evidence of violent crime — could be the primary instrument of criminal prosecution. IRS investigators and federal prosecutors assembled evidence from bank records, bookmakers' ledgers, and financial witnesses to prove Capone had received substantial income he failed to declare. The conviction sent Capone to federal prison and established forensic accountancy as a major tool of criminal investigation.

The Capone conviction through financial evidence had a significant literary dimension: it confirmed that the American gangster — who in hard-boiled fiction controlled through violence — could be brought down by paper evidence and bureaucratic investigation. This irony was not lost on American writers. The paper trail as instrument of justice became a recurring motif in twentieth-century American crime writing, and Capone himself became one of the most written-about figures in American popular literary culture.