Why would they need to know which room Sheila was found?
The room itself doesn't matter, just the fact that it was some way from the gun cupboard. It maybe looks less convincing if the crime scene has Sheila found in the kitchen or the den, for instance, as you could then interpret that as a deranged and confused Sheila putting the silencer back before killing herself, perhaps after first changing her mind and making to the den to put the weapon back, then changing her mind again. That seems less likely if she is in the bedroom, especially given that there was no blood evidence in the den - effectively ruling out Rivlin's explanation. If Rivlin was right and, let's say, Sheila had second thoughts, and then changed her mind again while putting the rifle back, then where is the blood?
Good point about also knowing which rifle was used. Some rifles won't have a silencer option. Also whether the silencer they chose was compatible with the murder weapon. I will add those to my list.
No problem Adam. It's the least I can do after you helped me out with the jet skis and also the other day when I was out in my windsurfing get-up. What am I like, eh, Adam?
They would need to know more than how to dismantle a silencer. They would also need to know how to create the back spatter effect. David even believes they learnt how to put diluted period blood into the silencer.
I disagree with you there. I see the logic in what you say, but I've already covered the point exhaustively above. There was no need for them to even know about back-spatter or even the range of the shots. Your reasoning is perfectly logical, but the basic flaw in it is that you are reasoning backwards from a conclusion. Remember the order in which the evidence was discovered, then think it through again.
I have no idea what the 'diluted period blood' is about. Maybe we should skip over that. My point about the blood is that, again, yes it is better if they know Sheila's blood group (and I think they did), but it wasn't necessary for them to know this to put in place an effective conspiracy given the state of forensic knowledge at that time, which they would have general knowledge of.
The reality is that they could just put any human blood in the silencer and it would incriminate Jeremy. If the blood group had matched, say, one of the twins, then all the better. At that point, Jeremy is in serious trouble.
You think it was 'lucky' that it matched Sheila. It was and it wasn't. On one level, it helped the police retroactively fit the silencer into the crime scene, but a clever defence barrister could have asked why, if a twin (or whatever other victim) were shot at contact range, that victim's blood type is not part of the blood grouped? If we accept drawback theory, then that makes no technically sense, though it does make sequential sense if you accept that Jeremy shot Sheila last (albeit he need not have).