Can you give us more reason as to why you're 100% sure the paper was not accessed? You don't need to tell us where it is/was, but your extreme certainty in that fact seems greater than the certainty I have about almost anything in my life.

Another possibility no one has mentioned yet: is it possible your nephew is lying? Perhaps he "stole" the cryptocurrency from himself, and went to his relative hoping they might give him pity money to get him back on his feet? Just a wild guess.