The Stone Killer (1973)

Top detective Lou Torrey is transferred to Los Angeles and uncovers a plot by a Sicilian mafioso to use Vietnam War veterans to murder all his enemies in a rerun of the "Sicilian Vespers" when the previous generation of Sicilian mafiosi were all killed on a single day. Torrey gets various clues that something big is about to happen, but will he discover what is planned before the big day?