It is further claimed by the prosecution he entered WHF by a window he was able to enter and exit undetected.
Was it possible for JB to have a contingency plan and early orderly exit if it all went horribly wrong in the early stages?
If he entered via the window (a familiar entry with family members) there was the potential for noise from opening the window and/or stumbling by mistake and/or the dogs barking etc. He gets in undetected then has to move about in the dark again avoiding any noise while removing the telephone from the cradle in the kitchen and gathering the gun and ammo (and silencer !?) which may have been where he claims he left them or in any other location if moved by others. Next he is tasked with moving upstairs to deal with arguably the greatest threat to his plan, controlling/killing NB. I do not know whether June and NB slept with the bedroom door open, closed or ajar? However it seems to me that up until this juncture if his plan went awry eg NB woke and/or others, JB could orchestrate an orderly exit by claiming that he was unable to sleep due to a sore throat/headache and was looking for some remedy as he had run out at Goldhanger. He could explain the gun in his possession by saying he thought he heard an intruder. Bizarre though it might sound he would know that anyone would struggle to demonstrate attempted murder at this juncture. Think OP.
Surely JB, a crack shot, would listen out for breathing/snoring as he crept up the stairs? If all was well ie no movement from the main bedroom he would gently open the door, if closed/ajar, and (POINT OF NO RETURN) disable/kill NB before he had an opportunity to leave his bed? The problem with this scenario is it does not afford an opportunity for the phone call from NB/JB's alibi of sorts. If NB was shot and killed in bed it would then prove difficult to stage NB's body in the bedroom as though he had made a phone call from there. If SC was going beserk with a gun anyone would be hard pressed to believe NB would make such a call lying down in bed or even sitting up in bed? (phone by NB's side of bed?) JB could have ordered/allowed NB out of bed and killed him in the bedroom to facilitate the phone call/alibi from the bedroom? Why did he waste vital seconds shooting June before disabling/controlling/killing NB?
Just who in the family other than Jeremy Bamber used the sliding-sash window to get inside WHF?
No doubt in my mind that the routine for getting in and out was well practiced by him several times before to make sure he could do silently (perhaps while the rest of the family were out). Having once lived in an old house with sliding-sash windows the wood frames tend to shrink over time making them easy to slide up and down quietly. The cast-iron counterweights boxed in on either side make the movement easier still.
Eyes become accustomed to seeing in the dark after a while and he knew the layout of WHF thoroughly because he was brought up there, so moving about inside presented no problem to him.
Why would JB even consider the plan going pear-shaped?
He couldn't allow the plan to fail because this was the only time the family would be gathered together at WHF perhaps before the following Christmas. Was it "Tonight's the night!" or "It's now or never!" that the told JM?
Why shoot June first? Because she was nearest when he entered to the bedroom door. The plan was to shoot both parents in quick succession.
Vital seconds are not lost with a semi-auto rifle like the Anschutz - you've seen the demo on Youtube...
https://www.youtube.com/watch?v=Bgz0lqGVouoAs soon as June was shot, Nevill's spontaneous reaction would to get up aqap to disarm whoever was firing at them, but he obviously didn't succeed. The kitchen phone fit-up was planned on the fly when the first scenario didn't work out as JB expected.
