St. Valentine's Day Massacre
During 1920's Prohibition, Chicago was embroiled in more gang-related gun violence than is found on the streets even today. One fateful Valentine's Day in 1929 saw Al Capone's outfit wipe out their rival Southside Irish Gang led by Bugs Moran.
Al Capone's men, disguised as Chicago Police officers, "arrested" members of Bugs' outfit in what initially appeared to be a standard "shake down." Seven men were lined up along the wall of an abandoned warehouse and summarily executed.