That's a good point. I thought of that. I did read one of the books about the case, the one by attorney William Kuntsler. It's been several years since I read it but from what I can remember, James Mills wasn't the brightest bulb on the tree. In fact, I seem to remember even the papers making comments about how clueless he was about everything. Of course, that doesn't mean he wasn't capable of murder. He could have just been playing dumb. I think he was questioned but I don't think they ever considered him a serious suspect.
My money is on the Reverend's family. I think they did get away with murder. Just the "personal" nature of the murders points to his wife and brothers, in my opinion, or at least someone who knew them. The fact that there was one of his calling cards left there placed at his feet, Eleanor Mills' hand placed on his thigh, torn up love letters scattered around them. And the fact that Eleanor definitely got the worst end of it, with her throat slashed and her tongue cut out besides being shot, to me that just sounds like something very personal that was originating from the Reverend's wife or family. It could have been her husband but after I read that book I just didn't see him as a viable suspect.
Now that I'm interested in the case again I might get the other book that was written called Fatal Tryst and see what conclusions that author comes up with.