My answer was assuming that this was the local police since he said local law enforcement. I guess I left too much to chance in my answer, but I know this was answered before. Yes, I agree, get a number from the person who has approached you--independently verify that the number is a law enforcement number. Just remember that just because someone answers the phone "Detective Jackson" does not mean that it is Detective Jackson you are speaking with. You may have to actually go to the police department and meet face to face. You don't want to blow an undercover operation, but you do need to make sure who you are dealing with.
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Better a patient man than a warrior, a man who controls his temper than one who takes a city