The silencer business makes no sense to me. Let's say that Jeremy shot Sheila with the silencer attached, and then he tried to put the gun in her hands to suggest she killed herself. That's when he realised that she couldn't have reached the trigger with the silencer attached.
What was he to do? He could take the silencer off and put it on the floor. That's what Sheila would have done. Oh, but then he thinks Sheila's blood might be on it or in it, so he can't do that. He comes up with a bright idea - he can put it back in the cupboard as if it had never been used. Suddenly, the idea that there might be blood on it doesn't matter. A day or two later he lets the relatives have a key to the house where he knows there's a silencer in a cupboard with Sheila's blood on it or in it.
Does that make sense?