Could just be Peabody, but I don't think so. I don't remember Harry noticing that Peabody's voice had any peculiar characteristics, just that he came off as an officious little twit. Jim likes to talk about what a lazy writer he is, that he doesn't put odd story details into a given novel just to throw them away later. I think if Madeline's contact was Peabody, Jim would have had Harry mention Peabody's odd manner of speaking or the strange way he pronounced certain words.
Also, this is still an unsolved mystery (one of many) within the greater story. There was also the clue of a telephone number in Madeline's phone to a restaurant in Cairo, Egypt. (If my memory is correct.) Somehow I don't think it would be good writing if sometime in a future Dresden novel we are told that two characters who died six, seven or eight books ago were actually working hand in hand. It reminds me of an idea of one forum member who was convinced that Maeve was the girl that Harry saw at Splattercon dressed up as a vampire before all hell broke loose at the convention. This person continued to post this idea long after Maeve got killed off at the end of Cold Days. (I suppose that could still be a relevant WAG if Harry breaks the Law against time travel by revisiting the events of Proven Guilty.) It was a fun WAG, but it's not relevant now that Maeve is dead, just as Peabody being Madeline's contact is no longer relevant for the same reason.
