If I was the detective in this situation I would start by seeing how long he was dead. From there I would ask where she has been and how she has been there. After that I would of asked her how long she has had the lamb leg in the oven. Her story wouldn't add up because she couldn't be out long if she was cooking. Also if the body was killed a couple of minutes after she started cooking she would of known who had done it but there was proof of anybody else in the building so therefore she would of had killed him with the frozen lamb leg and cook it and dispose of it by eating it.
