Playing on the 360.

So trying to complete Boethiah's Calling. Go in the cave and kill everyone stealthily. Nobody even THINKS I'm there. Save the Champion for last, obviously, and kill him stealthily as well. White (indicator) arrow disappears. I figure it's just a weird display issue and grab the Ebony Mail from his corpse and equip it.

Nothing.

Nobody is alive and nobody saw me. Why the Ned Flanders can't I complete this quest??