The narrator has a mental disease that made him kill the old man that he loved because he did not like his vulture eye. He was sent to a mental hospital because he is insane.
When he was in his bedroom, he decided the eye must go!
The narrator stalked the old man for seven nights at midnight to see if his eye was open. He would peek in very carefully, trying not to make any sound. He put in the lantern and would shine the light on the eye. One night he made a noise and scared the old man. He couldn't go back to sleep. The narrator stood still for an hour.
On the eighth night the lantern went on the eye and it was open. The narrator threw the bed over him and suffocated him until he was dead.
He took the body to the bath tub and chopped him into pieces, so there would be no blood evidence. Then the police came knocking on the door and the narrator let them in and search the house.
The narrator was hearing the heart of the old man and went crazy and confessed to the murder. Told them he was there under the floor.