What is the evidence that the narrator is guilty of the murder in the story of "The Tell Tale Heart"?

There is really never any doubt about the guilt of the mad
narrator in Edgar Allan Poe's classic short story, "The Tell-Tale Heart." The narrator
explicitly describes his actions, from his planning of the attack a week in advance to
the calculating way in which he completes his task. What the narrator refuses to admit
is that he is mad--not a murderer.

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... but why will you say that I am mad? The
disease had sharpened my senses—not destroyed—not dulled them. Above all was the sense
of hearing acute. I heard all things in the heaven and in the earth. I heard many things
in hell. How, then, am I mad? Hearken! and observe how healthily—how calmly I can tell
you the whole story.

The
narrator then gives his step-by-step process of the murder process. On the eighth night
of stealthily opening the old man's door and peering into his room, the narrator finally
takes action. When at last he saw the "vulture eye" open, the narrator
attacked.

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With a loud yell, I threw open the lantern and
leaped into the room. He shrieked once—once only. In an instant I dragged him to the
floor, and pulled the heavy bed over him... The old man was dead... Yes, he was stone,
stone dead... His eye would trouble me no
more.

Afterwards, the
narrator dismembered the corpse, placing it under the boards of the
floor.

The only argument against the narrator having killed
the old man would be if the old man had suffered a heart attack and died during the
process--a possibility that even the narrator refused
to consider.