One of the things that stand out to me with BG is why he would do it, if he did. The man was an attention seeking fantasist who wanted to be noticed. If he had killed her I would've thought it would be for notoriety, for the attention and 'fame'. I don't think he would've kept quiet about it - especially when he got convicted and essentially the game was up.
The question then is why JD? If he wanted to kill just to get the attention he could've picked anyone - as he had done with previous assaults. True, a celeb would give him more 'kudos' but with it the a lesser opportunity to carry out a murder. I would buy into the BG case if there was more evidence he had an obsession with her, but there wasn't anything. There is also no evidence of him stalking her (hard to do as he didn't drive), or lurking in the vicinity of her home before hand.
So what we have is a suspect who went out to kill that day and by chance came across the nation's number 1 TV presenter - true, they did live near each other, but the sheer luck of him walking down the street, at that exact time, just as she was about to go into her house (which gives us a window not of minutes, but almost seconds, to think, react and then carry out the crime) stretches possibility in my eyes.