In "The Cask of Amontillado" by Edgar Allan Poe, what is Montresor thinking when he says, "In pace, requiescat"? Please explain and use textual...

Montresor says this fifty years after having killed Fortunato: 

For the half of a century no mortal has disturbed them. In pace requiescat!  

It is ambiguous.

After fifty years, it seems likely that Montresor would have finally forgotten his anger towards Fortunato and that he would have forgiven the "thousand" injuries Fortunato imposed upon him. If that is the case, then the "rest in peace" sentiment might actually be genuine. In other words, by this point,...

Montresor says this fifty years after having killed Fortunato: 

For the half of a century no mortal has disturbed them. In pace requiescat!  

It is ambiguous.

After fifty years, it seems likely that Montresor would have finally forgotten his anger towards Fortunato and that he would have forgiven the "thousand" injuries Fortunato imposed upon him. If that is the case, then the "rest in peace" sentiment might actually be genuine. In other words, by this point, Montresor might actually be wishing peace upon Fortunato.

However, we could also read this sarcastically. Montresor has delighted in and even bragged about the methods he used to lure Fortunato to his death, so it is hard to read "rest in peace" without sensing some sarcasm as a fitting way to complete his scheme of revenge. 

Or, Montresor, old and close to death himself, might be saying "rest in peace" to himself. He has either finally gotten over the whole affair or he is still obsessing about it and trying desperately to achieve peace himself before he dies. Burying Fortunato might have been a symbolic way of burying some obsession in his own mind. Repressing it all these years and having done nothing to cure the psychosis, he still is obsessed and tries to invoke peace upon himself. 

There are a number of ways to interpret this final line. This might be a purposeful move by Poe. Montresor is clearly maniacal, a devious thinker. Leaving the final line ambiguous leaves the reader wondering what Montresor meant. Likewise, at the beginning of the story, the reader is left wondering what the "thousand injuries" or the insult were. It is a way of increasing the mystery of the story by invoking mystery about Montresor himself.