I too like IN THE STILL OF THE NIGHT, Joey. I believe that was the book I saw Miss Rule discussing on TV.
But SMALL SACRIFICES is such a great character study and Rule did such an amazing job of setting out her theory of the crime. I'm even open to the possibility she (Rule) may have been wrong (not about Downs' guilt, but about her motive); however, the point remains that the theory and character study are beautifully articulated.
(To be clear, I don't think Rule was wrong; her book is absolutely convincing. My point is that since I've done no independent research, I am happily just taking Rule's word for what was going on in Downs' mind.)