There's a nice story about a man who found $45k hidden in a house he bought from the family of an old man who recently died. He did the good thing, and gave the money to his family. Back in the 1970's, my family moved into a rather unique new house in a suburb of Cleveland Ohio. It was reputedly constructed by a mafia man, and had a fun rec room we called 'the ballroom' because it had floors for dancing with speakers and a bar with mirrors at one end. We bought it for $80k, which was slightly above market in my neighborhood, but nothing one would consider rich (not a prime residential neighborhood).
In any case, a couple years after we bought it, my dad was trimming the house, and found a $10 bill coming out of the molding connected to the roof. He went into the attic, looked in the floorboard near this $5, and found $5k in cash that were all dated from the 1950s. We didn't give it back, because it literally had blood on it, implying that its exposure might be unappreciated by the former homeowners. I remember how fun it was freshening up the old bills with a laundry iron. My mom's second career after raising me and my siblings was as an IRS agent, and she made me report my summer lawn mowing income, so this was her one little transgression against The Man.