How does not knowing what fortunato did to montresor intendify the horror of in the cask of amontillado?

Part of not knowing what Fortunato's crime against the narrator is adds to the horror because we do not know if it was something incredibly small or if Fortunato deserved it entirely, although his death was a crime in itself. Part of the terror is not knowing if the narrator is an insane, heinous murderer or a man with an agenda and a solid reason.  

Syllable added to a root word to change its meaning : affixan independent word--example run,walk,book : free morphemeaffix that gives grammatical meaning such as tense or number : inflectiona word part that must attach to a word in order to be usable : bound morphemedegree of comparison formed by adding -er or more to an adjective : comparativedegree of comparison formed by adding -est or most to an adjective : superlativeaffix added to the beginning of a word : prefixaffix added to the end of a word : suffixroot word of lovable : lovetwo roots used together to form one word : combining form