Try resurrecting him through console (open console, click the corpse, type "resurrect") and killing him again (maybe through console as well).
Sincerely, Yaell Novella (talk) 09:09, November 30, 2016 (UTC)
Tks for your input. Resurrect and Player.placeatme worked, but didn't work. Rising him again was not the issue. It seems the quest has to be done in sequence. So I had to go back to a good save and run the quest again in the proper sequence.