Is there proof that it was the killer weapon just because it was found on her body ?
No MORE so than had they seen someone standing over a body with a gun in their hand. However, in THIS case, we have to remember what preceded their find. A phone call from Jeremy relaying an alleged phone call fro Nevill saying Sheila had gone mad and got hold of a gun, followed by Jeremy giving them a full and somewhat exaggerated version of her mental history, her gun toting capabilities, and her previous suicide attempts. What were the supposed to conclude, when once inside a house secured from the inside, they discover a dead Sheila with a gun across her body? I don't care HOW often it's suggested. I DON'T believe it wuz Crispy!!!