If the blood staining was indicative of JB's involvement why didn't the prosecution use it?
As the COA decision shows they did use it but too late, they used it during the appeal. The prosecution experts didn't realize the blood/Bible issue until years later.
What the COA decision states is that the defense may have recognized the problem, thanked their lucky stars the prosecution was too stupid to see it and made the tactical decision not to raise the Bible issue because if the prosecution was forced to look at it in detail to try to undermine the defense then the light bulb finally might have gone off which is exactly what happened on appeal. Teh defense raised it and the prosecution had experts look and they said hey lookee here...
How do we know it was SC's blood and not June's?
The pool of blood is too much to be June's alone and is in a place that makes it virtually certain to be Sheila's. The bulk of the blood that was on the Bible came from such pool. It is always possible that some of the smaller amounts of blood was June's either by virtue of June walking over the Bible had she left it pen on the floor or Jeremy gotten some of her blood on his gloves and dripped a little from his gloves. That still doesn't undermine the argument made on appeal though which was that after blood got on it then it was closed and reopened to the same page and placed in the pool of sheila's blood that formed after her death.
How do we know June didn't walk round the bed holding the bible, with the blood originating from June, and she subsequently dropped it?
She would not have leaked blood walking with it at best she would have left finger prints. In the meantime if she dropped it then bled a few drops on it so what? It was still closed after that then reopened to the same exact page and placed in the pool of blood after Sheila was moved flat. What if anything the killer did with the Bible before moving her flat and sticking the gun on her is anyone's guess other than at some point closing it and reopening it.
There isn't any kind of evidence that could answer that other than Jeremy telling us exactly what he did. We can speculate why he reopened it and his steps but there are multiple possibilities so we can't be positive.
How do we know the perp didn't open the door between box room and main bedroom and cause the bible to concertina up and down thus causing the mirror staining?
The Bible would have to be much closer to the door to be hit. The location where it was found was protected from being hit by the door because the night table limited how far the door could open.
What difference does it make whether the Bible closed by getting hit by the door or picking it up and it closing? Why it closed makes no difference the fact it was closed and then reopened is what matters. Moreover what matters is that after being reopened it was placed in a pool of blood that formed after sheila died. Another thing significant is that it was placed near her neck instead of by her waist. If she had been reading it while sitting up then put it down she would put it by her waist. That's actually a stupid mistake but Jeremy wasn't thinking as clearly as he should have because of the excitement. That police and experts ignored such on the other hand demonstrates negligence. That's an easy one.
Given the bible was centre stage at SoC and JB's defence claim they were told the open pages were an unknown and/or the bible was missing why didn't they pursue this with the chief investigating officer and obtain something in writing to this effect?
Jeremy's defense made up that they were told the Bible was missing. It was a trial exhibit so they would have been able to examine it. The appeal court found their claim not credible and said their memory was faulty and for sure they could have examined it. In all likelihood they chose not to examine it because they didn't perceive any potential value or because they feared opening Pandora's box. On appeal they had nothing to lose in opening Pandora's box though they didn't make a very convincing argument that the page it was opened to constituted a suicide note or provided some proof of religious motive to kill everyone.
If there were a novel detailing murder suicide left near her that would be different then there would be a clear implication and the prosecution would have to claim it was planted.
On appeal the defense has nothing to lose. When the defense has a strong valid legal ground for appealing the defense will concentrate on such but if the defense lacks such then they pull out all the stops and argue anything they can no matter how remote the chance of success might be.
Let's pretend you are preparing for trial. How do you argue the Bible pages it was opened to were indicative of murder suicide? You can have the jury read the pages for themselves but that's about it. You can't have a theologian testify about the meaning unless you can show Sheila went to a theologian and have them say what she was told. Speculation is not of any value you would need what she was told or what she told someone she understood it to mean. On TV they show lawyers and witnesses being called to say things that in real life can't be said.
Only Jeremy knows what he saw the a passage on those pages that he decided to open it to such pages. For all we know he chose at random and just assumed they would say Bible = religious mania. We have no idea how much thought he put into it. Some things he overthought and some he under thought.
The most simple explanation of things is he placed the Bible on her or near her, got some blood on it in the process then decided to move her body to put the gun on her so moved it and it closed. Then after he was done putting the gun on her after the pool of blood formed he reopened it and stuck it in the pool.
Is this for sure what happened? All we know for sure is the Bible was closed and reopened to the same page and subsequently placed in her pool of blood. We don't know where it may have been moved from or why it was closed. We don't know if it was originally placed on her and some blood transferred to it from her gown before it was moved to the floor so the gun could be placed on her. There are many different possibilities and only Jeremy can tell us exactly what happened if he wanted to and he actually remembers. Given the passage of time he might not even remember all the details anymore in fact I would be shocked if he did.