What Michael says is "if history has taught us anything its that you can kill anyone." Since the Corleones were modeled on the Roman Empire, he could have meant anyone from Julius Caeser the Gracchi brothers, and everyone else assasinated before and since then.
"Io sono stanco, sono imbigliato, and I wan't everyone here to know, there ain't gonna be no trouble from me..Don Corleone..Cicc' a port!"
"I stood in the courtroom like a fool."
"I am Constanza: Lord of the idiots."
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