I've read this multiple times, and perhaps I'm being really thick, but I don't understand it at all. Can you elaborate? If the young man in the photo that the police released goes on to be identified as the alleged killer of Julia James, there's no way her murder could be linked to the Chillenden murders as he wouldn't have been born at the time (or barely).
The idea that there might be a DNA link between him and the sample recovered then is the stuff of fiction - unless you are saying that bludgeoning women out walking their dogs on a Tuesday afternoon is likely to be a heritable characteristic...?
What am I missing?