Al Capone was a turning point in history because he was the reason why alcohol became legal during the prohibition era. He made a lot of profiting from the trafficking of alcohol to prevent similar crimes involving trafficking liquor.
Despite committing murder and other crimes for years, it was the St. Valentine's Day Massacre that brought Capone to the attention of the federal government. When President Herbert Hoover learned about Capone, Hoover personally pushed for Capone's arrest.
http://dsc.discovery.com/tv-shows/other-shows/videos/assignment-discovery-al-capone.htm