The plot/trope where some crime so violent or egregious has happened that some alien/monster is automatically suspected to be behind it, only for our human protagonists to investigate, and in the end find out the culprits were actually humans has been used in a number of shows, e.g:
- Torchwood "Countrycide" (2006)
- Supernatural "The Benders" (2006)
- The X-Files "Home" (1996)
And probably many more.
What was the first work to feature this plot?
I'm looking for examples of something like the intersection of these two tropes: Human All Along (though perceived to be non-human for their violent actions, not their appearance, which is unknown) and Humans Are The Real Monsters
While interesting, examples where it turns out our protagonists (that we thought were human) are aliens, and the antagonists (that we thought were alien) were actually the humans, are not what I'm looking for!
e.g. Sentry, The Twilight Zone "The Invaders"