Later , rumors circulated that Cermak , not Roosevelt , had been the intended target , as his promise to clean up Chicago 's rampant lawlessness posed a threat to Al Capone and the Chicago organized crime syndicate . One of the first people to suggest the organized crime theory was reporter Walter Winchell , who happened to be in Miami the evening of the shooting . According to Roosevelt biographer Jean Edward Smith , there is no proof for this theory . Long-time Chicago newsman Len O'Connor offers a different view of the events surrounding the mayor 's assassination . He has written that aldermen Paddy Bauler and Charlie Weber informed him that relations between Cermak and FDR were strained because Cermak fought FDR 's nomination at the Democratic convention in Chicago . Author Ronald Humble offers another view as to why Cermak was killed . In his book '' Frank Nitti : The True Story of Chicago 's Notorious Enforcer '' , Humble contends that Cermak was as corrupt as Thompson and that the Chicago Outfit hired Zangara to kill Cermak in retaliation for Cermak 's attempt to murder Frank Nitti
Democratic convention in Chicago
1932 Democratic National Convention
Anton Cermak