Definitely had to be someone in the sorting center, the driver would have definitely delivered to the wrong house or not at all. I knew of a guy who used to work for FedEx in the sorting center a long time ago and he used to rip packages all the time. In fact it was as simple as you say, he would just follow the package to the loading area. Then sneak it off to be opened and emptied, I remember him saying that he had ripped at least 10 kilos in his time there not including the smoke he pulled. And the guy was serious, he had the money to back it up, he told me he would make an average of 25k extra a year going through stuff. The guy was a real prick though and I always thought of him as a thief, I have no idea where he is now, probably in prison.
KnB