I don't go out of my way to read of gruesome crimes, but I am a bit surprised that until yesterday, I don't recall reading about the "Bloody Benders", who bear the title "America's First Serial Killers".
A straight forward telling of their story, from 1870's Kansas, may be found here. Wikipedia has a fairly detailed entry, too.
What is particularly interesting, I think, is the link with Spiritualism, as well as the very "Sweeney Todd" aspect of victims being dumped into a cellar via a trap door in the floor.
As a medium, family member Kate was apparently giving out some rather unusual advice from the Spirit world. From the book Psychological Consequences of the Civil War:
I have to say, if your medium is giving out advice like that, I don't think it's wise to accept an invitation to dinner at home.
Anyway, it seems to me that this would be great source material for a film - especially given that it is not clear as to what happened to the family. Lots of room for speculation to be built into a screenplay "based on real events".