That is kind of also the setup in Knives Out though, to be fair - everybody thinks it's a natural death until someone sends an anonymous letter and fee to the Great Detective to investigate the 'murder'. So you can see why I was suspicious!!!

And yeah, you don't get into that kind of story unless you're in it for the ridiculous twistiness, preferably with lanterns hung on every turn, so I still don't think it's unreasonable that I always suspect the corpse first, especially when the dead person is presented as both endearingly eccentric and a massive fan of twisty murder mysteries. It's more likely than the butler! (Except when it's the butler and the corpse working together.)