There's your problem. You only know what they tell you.
So... you have a Sr. Manager that claims only one didn't take it, a Courier who KNOWS that they didn't take it (using up that "one" non-taker) and a "handful" of Couriers who claim they also didn't take it. Then there are all the other Couriers at the station in question whose status as to whether they took it or not is unknown...
Who is more credible, or more aptly put, is the Sr. Manager's account credible?
Three guesses as to whether the Sr. Manager is telling the truth or not. You'll only need to use one.
If you haven't figured out that FedEx management lies to the hourly employees as a routine matter of business, you really do need to have your head checked.
I caught FedEx management in a bold faced lie during my 2nd month of employment with Express. When I confronted the manager about it (Sr. Manager), they first tried to deny they lied about the issue, then when confronted with a witness who caught them in the same lie, started accusing me and the witness of not "understanding" what they really intended.
My comprehension of the spoken English language is excellent, along with my hearing and memory. This was the start of a long learning process on my part about what Express (and FedEx in general) was really about.