Your post got me to thinking about this again Tim.
When tests were carried out recently on a piece of pig skin it just didn't replicate the situation whereby someone is shot with a rifle at very close range. Is it not the case that when someone is shot with a rifle in such a way that there is back spatter? From what I have seen of the originals photographs there is no blood back spatter on Sheila's neck which leads me to conclude that when she was shot the rifle was not touching her neck but some inches away.
If this was indeed the case then there has to be another reason why Sheila's DNA and blood was found in the silencer. Could it be that whoever cleaned the silencer accidentally contaminated it with Sheila's blood?
So you go in,rifle at ready,silencer attached. Whatever order,all are shot. SC with the 1st shot. She is obviously shot upstairs. You've got to set the scene.you place the rifle in position.then the problem of the barrel is to long with the silencer attached.who knows,there may be many blood types on it.unscrew the silencer put it in your pocket.continue.
Problem.bloody silencer.take it home for "safe keeping". Mmmm.forgot to screw the knurled bit on the end mmm.
Problem.they surely going to notice the silencer is missing..... Better clean it up and put it back,they wil just think they will have missed it.
Now this is a possible chain of events,or maybe not. I will say however,that I've never been comfortable with the relatives finding the silencer.not so much the finding,more the taking position of.