First of all, let me say that Moose was the biggest problem in this whole case, but this PO box, was not for leads... In fact it was one of the few things Moose did, that might have caught these idiots. It didn't, but if the information that did catch the perps was not leaked, this might have.
The bar codes on the bottom of our mail has a great deal of information, and guess what, the post office has a record of your return address on mail that you send out (You, Grampa). (if you put it on)
Maybe someone here has a pointer to the details on this PO data collection scheme?)