The OP sent in the 1Z as missing, finds the package and rather than make service decides to bury it in with the send agains. Supervisor just happens to do a check-in audit, "missing" pkg is found, driver is terminated. I don't think I would want to be associated with any product that protects against such dishonesty.
I was asked to help a driver one day. He gave me a residential section to deliver, we transferred data between DIADs, I delivered the work only to find he had not given me one package. I sent in the 1Z (it was for a QVC Queen) and figured he would run it off on his way back to the center. The center manager figured the same so when the pkg showed as undelivered they did a "random" check-in audit of his car. Found the pkg buried in his pickups. I think he was given a one-day suspension over that one.
The OP will be offered a suspension, time served, no back pay, back to work as early as Monday.