I've been watching (the first series of) Only Murders in the Building and, together with hearing a friend listening to an Australian thing about a kidnapped and presumably murdered girl, it got me thinking about True Crime things (normally podcasts). I've read that, contrary to what one might immediately assume without considering it properly, that the audience for True Crime stories and those for detective stories actually have relatively little overlap. I suppose this applies specifically to ones dealing with unsolved crimes, as they were talking about how although on the surface, they are both similar sorts of things, the appeal with Poirot or whatever is the neat packaging up of the mystery and its loose ends into one perfect box, a jigsaw puzzle in which every piece fits, whereas with an unsolved murder the opposite is the case.
And from my own limited experience I can see that they are often incredibly frustrating; when you read stuff about Jack the Ripper for example and the descriptions reveal a well to do, tall, cleanshaven redhead of middling height with a large bushy black beard and in ragged dirty clothes you want to throw the book at the wall. When you realise that they can't even agree about what the writing about Juwes (or whatever it was) - which may or may not have been an uncrucial non-clue - said and that there was no definitive copy made before they incredibly irritatingly wiped it off the wall with an uncharacteristic efficiency that was never matched at any other part of the investigation then you start to feel that someone is taking the piss. Real life is not just messy and lacking in resolution, at times it feels like a deliberate assault on objectivity.
And this is why, to me, in a sense it does feel as though it might be the natural end-point of the detective arc. If first we had perfect inhuman reasoning machines such as Holmes, and then fallibility and doubt crept in, detectives who are scarcely better than the murderers they put away, corrupt police departments... even corrupt protagonists who manage one moment of decency, increasing amounts of unexplained elements and criminals who get away... perhaps this is the answer to my original question about whether the detective just goes on for ever, whether it truly is a 20th century character, or if the detective story is, as at one point it appeared, going to keep growing so much it simply absorbs all other genres.
So maybe it started just before the 20th century with a perfect detective in Edgar Allen Poe, continued with Holmes and then got more and more realistic and fallible, to the point that only true crime was realistic enough and, by the end of the 20th century, it had evolved to the extent that it no longer had any of the stuff about it that its fans liked and had become something totally different. Of course the true detective struggles on, as real rock music did after punk but maybe it has also lost its vitality and will be argued for by "real" fans who think that "solving crime isn't dead" or we need to get back to the old skool cos we did it right the first time.
Or maybe that's also too neat. One way out is things such as Only Murders in the Building which simulates a true crime podcast but will (I assume, I haven't finished it yet) tie everything up as neatly as Father Brown ever did. A perfect way to fight back, and of course for it to have its cake and eat it.