"The Tell Tale Heart" by Edgar Allen Poe.

An unknown narrator starts the story by telling us that he is not mad. He says that he is going to tell a story and his confession of having killed an old man. His motivation for the action was the old man’s vulture blue eye. Every night, he went to the old man’s house and observed the man sleeping. In the morning, he would behave to the old man as if everything were normal. After a week, he decides that the time has come to kill the old man.
When the narrator arrives on the eighth night, the old man wakes up and cries out. The narrator remains silent, watching the old man as he sits awake and was terrified. Soon, the narrator hears the frightened heartbeat of the man. Worried that a neighbor might hear the loud thumping of the old man's heart, he attacks and kills the old man. He then cut into pieces the body and hides the pieces below the floorboards in the bedroom. He is careful not to leave even a drop of blood on the floor. As he finishes his job, a clock strikes the hour of four. At the same time, the narrator hears a knock at the street door. The police have arrived, having been called by a neighbor who heard the old man shriek. The narrator remains normal. He leads the officers all over the house. At the height of his confidence, he even brings them into the old man’s bedroom to sit down and talk at the scene of the crime. The policemen do not suspect a thing. The narrator is comfortable until he starts to hear a low thumping sound of the heart of the old man from underneath the floor. He recognizes the low sound as the heart of the old man.
He becomes nervous and believing that the policemen will also hear the sound and will know his crime. Driven mad by the idea that they are mocking him with their pleasant chat, he confesses to the crime and shrieks at the men to rip up the floorboards to get the dead body of the old man which was present in the chopped form.