How is the theme of discovery developed in Poe's "The Tell Tale Heart"?

Poe's story is about secrets -- secret feelings, and secret deeds. So, if we think about discovery as "finding" something, in a way the story is about the fear of being "found out" or discovered. There are many examples of this in the story. From the beginning, we as readers are put in the position of having already "found out" something about the narrator -- the narrator is addressing us, and the story begins in mid-conversation, as if we already have discovered his madness: "Why do you say that I am mad?" In the part of the story where he looks in on the old man in the night, the narrator is specifically trying to avoid detection or discovery -- "He could not guess that every night, just at twelve, I looked in at him as he slept." But it is the night that he is detected in the dark, looking down at the old man, and his "discovery" in the faint gleam of the lamp of the old man's "vulture eye" -- that actually causes th narrator to murder him. The secret of of the murder must be concealed -- the body of the old man is hacked up and hidden under the floorboards -- but the secret cannot be concealed from the police for long. It is the narrator himself who makes the discovery of the body for the police -- the hallucinatory sound of the beating heart driving him to do it. Perhaps the particular nature of the narrator's madness is a morbid need to reveal all his secrets -- the deeper the secret, the greater the need for discovery.