After killing the old man, the narrator believes he is proving his sanity even more when he silently and quickly dissembles the body in the bathtub.
Then, the narrator opens the floor boards and hides the evidence by burying the body parts. Finally, he precisely puts the floor boards back as if nothing ever happened.
All of a sudden there was a knock at the door. The cops showed up from a neighbors noise complaint. Instead of being nervous the narrator was the total opposite. Knowing he had got rid of all the evidence the narrator gladly welcomed the cops in.
The narrator led the cops upstairs to investigate. He was so confident that he brought up a chair and sat right where the body was buried. The narrator showed no suspicion and was having a normal conversation with the cops.
As they were talking the narrator believed he could hear the heartbeat of the old man. The beating of the heart grew louder and louder in his head and his skin grew pale. The narrator started speaking fast with large gestures. The beating got so intense he believed the cops could hear it too.
In the end, the narrator's anxiety took the best of him. He stood up and showed the cops where he buried the body. The narrator had took so many precautions to getting rid of evidence but to only turn himself in at the end.