The vampire did admit, that he killed George, something about that George wasn't useful to him anymore and in the quest journal, there is the entry to go report to Mardaneus, it's just that I can't report it, because the option isn't there, the questlog entry is as it should be, but advancing the quest isn't possible for some reason. The quest in Verdistis is solved, I've successfully reported to Kratus, but not the one in Aleroth, can't report to Mardaneus, regardless what the questlog entry says.