Here is a thought-provoking post from author Christopher Lansdown’s website:
Dysfunctional Families in Murder Mysteries
I was recently watching the Murder, She Wroteepisode It’s a Dog’s Life with my eldest son and it occurred to just how much dysfunctional wealthy families are a staple of murder mysteries.
It’s not the wealthy part that’s at all surprising—it’s well known that the two most common motives for murder in detective fiction are sex and money—but the dysfunctional part. Or at least that they’re obviously dysfunctional.
This is probably more a staple of modern detective fiction like Murder, She Wrote than it is of golden age detective fiction, I should add, though one can certainly find it in golden age detective fiction too.