Did they die mid-spree? Because, as you say, it is rare indeed for a true serial killer to stop rather than escalate.
I know almost nothing about the Yorkshire Ripper... I had heard about his dying, and had read his Wikipedia article. Jack The Ripper I have read about somewhat extensively... but the problem with old cases like that, which pertains to the Zodiac as well, is that with time come the myths and legends until it is difficult to distinguish the actual facts of what they knew, suspected, and what vivid imagination has introduced.
I remember reading a book a short time back in which a guy was claiming Zodiac was his Dad.... only a few pages in I realized it was a lot of nonsense. Even the definitive book about the Zodiac written by, Robert Graysmith, has now been picked to pieces revealing some very inaccurate details.
