Drama Queen,
I was fairly certain that the privacy act allows a bank to share customer financial information with law enforcement only in pursuit of criminal cases that it has filed (i.e. when it is the victim), and when requested with proper subpoena. Of course, some state laws override this for local law enforcement (GA being on example I've seen given).
As Greg points out, they will try to cut procedural corners whether in attempt to speed things up, lack of knowledge concerning laws that they probably don't deal with that often, or plain human nature and the inclination to follow the path of least resistance. Regardless, it seems to me like the paperwork would be less frustration than jeopardizing what might be key evidence.
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The above is my opinion, and is frequently valued at USD 2¢ or less.