It would seem that Amazon would just pay them to return to the warehouse with merchandise, rather than paying them for each package they don't deliver.
Given Amazon's razor thin margins, zeal for efficiency and cost consciousness, this seems to just be a suspect making up a story to try and get away with a crime.
Not only that. Amazon is aware of which packages it’s given to a delivery driver. If he returned packages that weren’t given to him that’s a major red flag.