Run for the hills.
Besides calling the authorities, what would you do if you were doing renovations and you found a skeleton in the walls of your house?
For sale sign.
First I would gasp or scream. After the investigation have the house blessed. Then finish the renovations and sell the house.
Hang some new sheetrock and call it a day. :)
Send me your email address and I'll send you the story of "The House". No actual skeletons - But some other quite spooky stuff.
Well, I would just hope there really were a "cask of amontillado" with that skeleton.
(Personally, I woujld prefer an oleroso.)
Sell the property at first available opportunity.