"The butler did it" is a common trope indicating a hackneyed solution to a mystery. I have read several classic mysteries from the 1920s and earlier (Poe, Conan Doyle, Christie, Sayers, etc.) but do not recall a single instance of the butler's actually being the criminal mastermind, let alone enough such stories to justify the phrase's use as a cliché. The one example I can think of, Agatha Christie's 1925 short story "The Listerdale Mystery," plays with the trope rather than using it straightforwardly.
TV Tropes claims that the idea of the butler as perp was already clichéd by 1928. But the page gives no little evidence for this. The page discusses two origins for the phrase, both dubious:
- It is often attributed to Mary Roberts Rinehardt's The Door (1930). But the page also says that the phrase does not actually occur in the book.
- It is part of rule #20 in S. S. Van Dine's 1928 essay "Twenty Rules for Writing Detective Stories." But criminal butlers are not mentioned in that rule, nor anywhere else in the essay as far as I can see.
In any case, TV Tropes treats the idea of "the butler did it" as cliché rather than discussing what led to its being seen as a cliché in the first place. Google Ngrams shows that the phrase was practically unknown before the 1920s and then jumped in usage:
But what led to this increase in the phrase's use? What mystery books or stories from the early days of the genre had the butler as the perpetrator of the crime, leading to this plot device becoming a cliché?
Note: this is not off-topic as asking for a list, because I'm not asking for recommendations. This is more along the lines of the many "What is the earliest example of X?" questions asked on this site before. The only difference is that I'm asking for a series of early examples rather than just one, because the sheer number of examples evidently led to this becoming an undesirable way to structure a mystery plot.