They’re not really legally binding because (as far as I know) for a legally binding agreement to exist, both parties must agree to the terms and conditions. Such email disclaimers are not agreed to by both parties (well they try to make you agree by using wording such as “By reading the email, you agree to XYZ”, but again that’s not really you agreeing at all, that’s them making you believe that you agree to the terms).
Here’s a great Slate article that goes into detail about one such disclaimer, breaking down each line. In that disclaimer’s case, it was mostly fluff and requests (“should”, “may”, “please”). As with all other law, such weasel words really add a dimension of confusion. Then again, that’s what lawyers want – if the law was simple and easy to understand, fewer lawyers would be hired.
In your hypothetical case of forwarding information about a crime to the police, I highly doubt that the disclaimer would get the criminals off the hook. The police department doesn’t usually use one piece of evidence submitted by a citizen, they will take your lead and conduct their own investigation, and then press charges based on the result of their investigation. I’m sure the criminal’s lawyer, if they found out about the email lead, would certainly try to have the case dismissed based on the disclaimer, but I highly doubt that would be successful.