I'm hesitant to advise my clients to ever take a polygraph because the reading could be wrong. If I were you, I would sit down with an attorney before you consent to taking one!
Theft by deception, 18 Pa.C.S. section 3922, occurs is a person "intentionally obtains or withholds property of another by deception. A person deceives if he intentionally:
(1) creates or reinforces a false impression, including false impressions as to law, value, intention or other state of mind; but deception as to a person's intention to perform a promise shall not be inferred from the fact alone that he did not subsequently perform the promise;
(2) prevents another from acquiring information which would affect his judgment of a transaction; or
(3) fails to correct a false impression which the deceiver previously created or reinforced, or which the deceiver knows to be influencing another to whom he stands in a fiduciary or confidential relationship.
If the cop thinks the money never existed, I'm not sure where theft of *anything* is relevant. If he thinks you lied in reporting the money as stolen, then you could be charged with filing a false police report, but I don't see theft by deception here.
If charged with anything, I suggest you consult with an attorney immediately and don't talk to the cops anymore until you do! Best of luck to you.
Cary B. Hall, Esquire
Law Offices of Cary B. Hall, L.L.C.
121 East Chestnut Street, Suite 205
Souderton, PA 18964
T: (267) 663-9995
F: (215) 525-4364