Done quite a lot of YT viewing tonight, one documentary was regarding the Sally Anne Bowman case as referenced earlier. There we had a young girl, dropped by her on-off boyfriend practically to the door, and she was murdered (and then sexually assaulted - in that order unfortunately
) and left in a pool of her own blood on the doorstep. In that case, quite rightly so, the boyfriend was the prime suspect until DNA evidence showed up the real perp, however it still took 9 months to bring him to justice, and as said before, it was quite by the off chance.
Then I watched quite an old programme, called 'Crocodile Tears' (think there has been a more recent show called 'Tears, Lies and Videotapes') which focused on killers who had made appeals, only to later be found guilty of murder. It was extremely interesting. Link here:
http://www.youtube.com/user/RealCrimeUK#p/c/2474E6888EE26957/0/0kE9GuagWZU
I think what it has made me conclude is that I am almost 99.9% sure that this was not a stranger/opportunist murder. There would have been no reason to move the body if so, and how many opportunists have cars which can be spotted? Much easier, if you're going to prowl, to be on foot, where you can be hidden away in the shadows. I'm going to assume that Joanna's killer had a car, of which to dispose of her body.
What the above documentaries also made me realise is that police can and do suspect from the off, but cannot arrest until they have solid proof. For this reason, and the fact that the LE are being so vague with the information they give the public, I am of the same thought that the police know who did this and are currently trawling through masses of evidence in an attempt to have enough for an arrest.