... but rarely does.
No way I can tell from the information here alone, but the contents may have been taken by someone in the delivering post office. This is a case where the Postal Inspectors should be looking for the thief when a package is found to be rifled in house. It shouldn't be hard to find who was on the route the day it came in, and when he knew the contents were missing.
We would have called the Inspectors in on it right away, and the local office may have, but isn't saying anything until they have some kind of results. I suggest going to the USPS website and contacting the Postal Inspectors directly.
www.usps.com