I need evidence that the story "The Cask of Amontillado" begins in medias res.

In medias res, or “into the middle of
things” is Latin phrase used to describe a story that begins in the middle or even at
the conclusion instead of at the beginning.

The main character and
narrator of the story, Montresor, relates his story of revenge to an unnamed listener,
the mysterious “you” who is acquainted with Montresor. He narrates his story in the past
tense, referring to events that have already happened. 

Finally, the
clearest clue that Montresor is looking back and telling the story after the fact comes
at the very end with these statements:

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I forced the last stone into its position; I
plastered it up. Against the new masonry I reerected the old rampart of bones. For the
half of a century no mortal has disturbed
them.

With the final
sentence, we know that Montresor’s revenge happened fifty years ago--and no one has
found and disturbed Forunato’s tomb since Montresor buried Fortunato alive in the
wall.