Either he doesn't spawn, or is instantly killed by the spirits when entering, so you can't turn it in.
I believe he spawns on a trigger somewhere between the last three corners which is easy to miss when you're running along the edge of the corridors trying to avoid... Stuff.... one can or can't see, though I've had personally one instance where I couldn't get the boss to show up at all.
Though on another note I believe the ghouls that are supposed to be his friends attack him as well so it's like a 3-way Battle when he does show up.
The quest completes if NPCs kill him.