Please remember to post a SPOILER tag in the title of a thread like this, just as the sticky thread recommends. I'll change this one. You're on your own, afterwards.
There is a glitch in this quest, by the way. Sometimes, the body simply isn't in the well. If that's the case here, you may need to use a console command. Be sure to create a new save, first, before you attempt this.
Hit the ~ key. This should bring up the console. Type in:
sqt
Hit return. This should give you a quest ID. Now type:
completequest <questID>
Hit return again. Close the console. That quest should now be finished, and you should be able to return to the quest giver.