Is this supposed to prove that he killed somebody?
Perhaps not on it's own but that's not the point. It's the accumulation of evidence.
Oswald makes a special trip to Irving mid week and takes a long package to work.
Oswald leaves all his money with Marina and symbolically leaves his wedding ring in her family's cup.
Oswald tells Frazier the package contained curtain rods, Oswald says while being interrogated that he only brought his lunch.
Knowing the package is too big to place on his lap, Oswald places it on the back seat where Frazier sees it, but tells the Police he carried his lunch with him up front.
An empty long package is found with Oswald's prints in the sniper's nest.
Nobody says that Oswald is seen with a long package at any time after Oswald leaves work.
JohnM