Mwa ha ha, I got it right!
For a moment I thought it was something to do with jealousy, as if the sister had done something relating to the man, but I knew that that couldn't be the answer as the story does not give this information. I linked the sister's death to the mother's death, and voila.
Who says we have the mind of a psychopath? Could be the mind of a detective as well. [img]smile.gif[/img]