With the Resurrect skill active, moving the cursor over the body of an NPC should pop up a name/class (orc, etc). Right clicking will bring them back to life, with a friendly alignment. If you leave the area they will turn hostile, and you can return to kill them again. Otherwise, you can use Aura of Command to get them to follow you.
There is/was a skull on top of the chest; drag it into your inventory, and try the chest again...
