They don't have to tell us who did it. Not for sure, definitively, answer *all* the questions, with pictures with the circles and the arrows outlining each crime.
They can tell us who the Girl Twin is. And other relevant secret character tie-ins.
And still leave some murders unsolved. Frex: Cast doubt on whether the same 3 RDs killed everyone, suggest Hester/Grace/#5 "got away with" something by a sly wink to the camera, and end the Season.
Season 2 features - the characters or the actors, which is it? Actors stay, characters go, right?
( I swear to god if I am still arguing about this next season because we don't know for sure, I'll be forced to cancel the internet if I ever want to sleep again).