Here's one, one only lawyers would know:
In Collateral.....
SPOILER TO FOLLOW
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In Collateral, Vincent is on a trip through LA offing witnesses to a big federal drug trial. His last hit is the prosecutor on the case for the DOJ. Anyone who has worked at DOJ can tell you that there are three main attorneys assigned to every case. They all know everything about the case, and split the workload -- one will do the opening, one will do witnesses X,Y,Z, etc. etc.
So, offing one prosecutor would do no good, as the other two would be able to pick right up where the one was absent. Factual flaw.