It is possible that Mr. Sonder made the whole thing up, but Dutch officials in charge of the search thought this was unlikely, documents indicate. Another theory is that one or more of the government searchers had secretly already found it. And yet another — and what some people consider to be the most likely — possibility is that one of the Nazi soldiers who hid the treasure went back and quietly unearthed it himself. No scenario has been proved, and it is unclear whether Mr. Sonder is still alive. It is not the first time that the village, which...