Murray Humphreys late 1920s to the early 1930s, Humphreys, along with "Red" Barker, William "Three-Fingered Jack" White and William "Klondike" O'Donnell, was one of the mobsters who orchestrated the Outfit's takeover of a number of Chicago labor unions. Humphreys was later indicted for the December 1931 kidnapping of a union president, Robert G. Fitche, but escaped conviction. In 1933, with Capone behind bars for income tax evasion, the chief investigator for the State Attorney's office described Murray Humphreys as "'public enemy No. 1' and 'the czar of business rackets in Chicago.'" Later that same year, Humphreys was indicted for income tax evasion
Tax evasion in the United States based on total positive income. Using line items from the auditor's checksheet, discriminant analysis, and a scoring mechanism, each return was awarded a score, known as a "Z-score". Higher Z-scores were associated by IRS personnel with a higher risk of tax evasion. However, the Discriminant Index Function (DIF) system did not provide examiners with specific problematic variables or reasons for the high score and so each filing had to be manually examined by an auditor. The IRS may carry out investigations to determine the correctness of any tax return and collect necessary income tax, including requiring the taxpayer to provide