who did the shooting? Isn't there some charge for withholding evidence after a crime? I think something like "accessory to .... after the fact..."
If the witness won't talk, and there's no criminal charge to which he can be cited, perhaps the responding officers could stop in the neighborhood for regular updates. Sooner or later, the shooter(s) will think he's talked, and make a move OR the witness will speak while he still has time before the shooter(s) take some action.
Used to work in the movies anyway.
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