So there's a knock, but no package or even a delivery notice? Do you live in an apartment complex? Do you have a history of receiving regular deliveries where it's been established that it's ok to leave packages without requiring a confirmation signature?
Just trying to get an idea of your situation since what you are describing is what delivery personnel are told to do by such companies. And if there was no package or delivery notice, how do you know it was a FedEx driver if there was no one to be seen by the time you opened the door?
Not defending FedEx or that particular driver, but something just seems to be missing from the situation you described. My past experience with UPS was only part time, but even in that time I became aware that there were "usual" routines that had been established between drivers and some repeat customers.