I was fairly sure a similar thing was happening at our old house. Over a couple of weeks, I had 3 packages that never showed up, even though the other parties sent them and in one case I had a DC# stating that it had been delivered. Personally, I suspected someone from the neighborhood just grabbing the packages (I work at a home office and frequently have office equipment & stuff delivered).

Strange part was that it was a pretty good suburban neighborhood. No place is safe, I guess.