This is an example of FFC and Puzo showing us how ruthless Michael Corleone had become:
Woltz rejected Vito's offer in almost the same way that Geary rejected Michael's proposition, including ethnic insults ("guinea Mafia goombah," vs. "oily hair, silk suits, pass yourselves off as decent Americans"). Vito killed a horse to make his point on Woltz, Michael had a hooker killed to force his on Geary. When Vito was in charge, no civilians were killed in family wars, and Clemenza told Sonny that it was safe for Michael to visit Kay in NYC because "Sollozzo knows he's a civilian." By the end of the film, Michael's Great Massacre of 1955 saw the murder of a hooker in bed with Tattaglia; a chauffer and bodyguard with Barzini (the chauffer possibly a civilian), and (probably) the elevator operator in the elevator with Stracchi. You might argue that all those civilians were "incidental casualties" (wrong place, wrong time). But, in GFII, Michael planned the murder of the hooker for the sole purpose of snaring Geary.