Oh do stop being cryptic al. If you have a theory pray tell or keep quiet until you are in a position to 'enligten' us with your insights 
I thought I explained my theory already. Maybe that was on another board. Well, here it is again. Still a work in progress but:
1 he murdered everybody
2 he called his own number from WHF at 3.00 a.m. a pre-agreed time with Julie
3 he hung up once the answer phone kicked in, thus ensuring, as he thought, BT would have a record of the call
4 he called Julie's number a minute or two later, again by prior arrangement
5 he interrupted the call before it was answered so BT would
not have a trace of it
6 he went home
7 Julie (this is part of their plan) went into SB's room to discuss the call she had not, in fact, answered
8 SB noted the time on her clock as being 3.12, adjusted to 3.02, which fits perfectly with point 4 above. I bet Julie said something seemingly innocent about the time to cause SB to notice it
9 JB cycles home like crazy, takes a quick shower, discarding his clothes and towels somewhere with a view to permanent disposal later
10 JB calls Witham/Wickham Bishop and then Chelmsford having some time beforehand, when preparing the crime, circled the number(s) in the phone book (this is a prediction based on a combination of (i) faint recollection of reading that he did that and (ii) an appreciation of his scheme)
11 he has a private meeting with Julie when she showed up in the morning in order to agree some aspect of their stories (e.g. whether he called her before the police or after)
It all fits. Case closed.
