If you or I, or anybody had been the person who had shot and killed Sheila with a single shot under the chin, and we had left her for dead on the bed (as described), and we had set about stage managing her body by placing a rifle upon it, and then positioning her hands upon and around the gun, so as to make it look like she must have taken her own life, and we were later arrested and charged with her murder, stood trial for it, as Jeremy did, we would know that the prosecutions case as relied upon at trial was a false one, because Sheila had not been killed by us, you, me, or anybody else for that / this matter, and left for dead there on the bed with a solitary wound to the neck, but her body ends up on the bedroom floor with an additional bullet hole in the neck, and the gun now on top of her body on the bedroom floor, and her hands conveniently repositioned upon and around the gun, in a different location inside the bedroom from where we, I, or us had stage managed her body on the bed, with a view to making people think that she had taken her own life, in the same way we, you, I, us had originally left her...
If we, you, I, or us had killed Sheila and stage managed her body on the bed, at a time when she only had a solitary wound upon her neck, and we end up in court charged with involvement in her murder, and the case against us, includes for the fact that Sheila was shot twice in the neck, and her body had been stage managed on the bedroom floor to try to give the impression that she had taken her own life there, we would know, you, I, us, that somehow Sheila had been shot a second time in the neck, and that somehow her body got moved from the bed to the floor, and re-staged there, with a similar intention of someone trying to make it look like she had taken her own life - at the heart of this matter would be, is the fact that (a) there has been an additional shot fired into the victims neck, (b) the victims body has been moved from the bed to the floor, (c) the body has been re-staged a second time, by someone else, on the bedroom floor...
If we, you, I, us, had been the killer, and we faced trial in the connection with Sheila's death, we would know how to defend ourselves against the allegation that we had shot Sheila twice in the neck to kill her on the bedroom floor, and stage managed her body there, so as to get the police thinking she had taken her own life there and then, as outlined...
Now...
Either the police shot her the second time and they stage managed her body on the bedroom floor, or as the case may be, Sheila did kill herself there, where police later photographed her body - nothing could be any clearer...