In no other time in history was the line blurred between lawmen and criminals as it was during Prohibition. It was often difficult to tell one from the other since their relationship became symbiotic. Gangsters helped political candidates, such as Mayor William Hale Thompson of Chicago, get elected to office. And in return, corrupt politicians issued permits to bootleggers or turned a blind eye to their operations.

The problem worsened after the onset of the Great Depression in 1929. Towering unemployment and the public's frustration with government contributed to the delinquency of ordinary citizens. Many of these citizens had never broken the law before and clogged up the legal system after being caught. Ironically, they were sometimes acquitted by sympathetic juries who also believed the law to be unjust.

On the streets of major cities across the country, gangland murders were on the...