Of course you need to remove this critter. Then simply using any spray such as commercial sprays should do the trick.. if the animal has leached into the walls, or floor a more aggressive method will be required. On drywall removal of the material is in order. For items such as cement. Flooding the floor with bleach will do the trick.
Unable to locate the deceased (in attic). Odor gradually is dissipating.
You would be surprised on how small a critter can make such a large odor. We had a mouse that climbed into our kitchen vent and made its way to the top of the vent hood were it died. Phew did it stink. Once removed the odor was gone.