Why did the neighbours immediately call the cops? Did they already know he was guilty? Were the cops making him go insane at the end? Did the cops suspect him before he admitted it? What is wrong with the narrator mentally? Is he even human?
I feel that the missing word is most likely "lens" - check if it's among your options.
When something is compared to a lens through which the word is seen, it means that the world is seen through a certain perspective, that it's using a certain interpretation: here that of literary theory.
<span />