Missing Evidence

Charge: prescribing a narcotic to persons not under treatment for a pathology. The state seeks to introduce evidence that during the preliminary hearing the clerk permitted Dr. D to examine the exhibits and later discovered that the prescriptions were missing. Pieces of the prescriptions were subsequently found floating in a toilet bowl in the courthouse rest room. D objects on grounds of relevancy.

What ruling and why? What chain of inferences does the prosecution want the jury to create in considering this evidence?