Answer:
The element of the above passage which helps the reader to infer that the narrator might be insane and without morals is the businesslike tone in which he is speaking.
Step-by-step explanation:
In the above passage, the author sets the plan of the murder in a much professional way. His tone is all set in a tone as he was set for this particular task. After completing the act of murder, the narrator is now thinking about the decomposing of the body.