One question (among many) that really stands out to me: Since this treasure was allegedly hidden off his property for anyone to find and the treasure was supposedly all present in the box (not a case of you find the box and inside is contact information for you to go and claim the prize), why would ANYONE in their right mind disclose they found it, save for perhaps a few ego centric people who seek the limelight or think they can profit from it (appearances, a movie, a book etc).
It's documented the guy who found it didn't want publicity, so why ever come forward in the first place?
At a minimum if he felt like letting the depositor know he found the treasure so the search could be called off, he could just anonymously contact him.