Complex sentence: Alterie by some reports killed more than 20 Outfit and Genna gang members during this conflict which had erupted into a full-scale gang war in 1924 when O'Banion was murdered by Outfit gunmen in his floral shop on State Street in Chicago.
Split into simpler sentences: Alterie by some reports killed more than 20 Outfit and Genna gang members during this period. In 1924, the conflict became a full-scale gang war when O'Banion was murdered by Outfit gunmen in his floral shop on State Street in Chicago.