From Citizendium, the Citizens' Compendium
The Purple Gang was a gangland mob operating in Detroit, Michigan, during the prohibition era in the U.S. It was led by a group of Jewish brothers and, unlike other major Jewish criminal organizations, the Purple Gang was the only one to solely control the organized crime of a major U.S. city. They were particularly ruthless at controlling the Detroit River waterfront which was a choke-point for the importation of bootleg liquor during prohibition. It has been rumored that they had committed over 500 murders, which, if true, would make them more ruthless than Al Capone's mob. They have also been rumored to have been the masterminds behind the Lindbergh baby kidnapping and the St. Valentine's Day Massacre.
The gang was broken up by law enforcement and internal violence. Various members were arrested, and tried for crimes (mostly murder) and sentenced for varying terms (some to life in Alcatraz). Others were gunned down. Most of the leadership of the Purple Gang were either dead or in prison by the late 1930s.