"Mister D'Arcy is not a policeman. He is, however, very wise. He knew the police would search his apartment. He also knew how police think. So, he did not hide the letter where he knew they would look for it. "Do you remember how Germont laughed when I said the mystery was difficult for him to solve because it was so simple?" Dupin filled his pipe with tobacco and lit it. "Well, the more I thought about it, the more I realized the police could not find the letter because D'Arcy had not hidden it at all. "So I went to visit D'Arcy in his apartment. I took a pair of dark green eyeglasses with me. I explained to him that I was having trouble with my eyes and needed to wear the dark glasses at all times. He believed me. The glasses permitted me to look around the apartment while I seemed only to be talking to him. "I paid special attention to a large desk where there were a lot of papers and books. However, I saw nothing suspicious there. After a few minutes, however, I noticed a small shelf over the fireplace. A few postcards and a letter were lying on the shelf. The letter looked very old and dirty. "As soon as I saw this letter, I decided it must be the one I was looking for. It must be, even though it was completely different from the one Germont had described. "This letter had a large green stamp on it. The address was written in small letters in blue ink. I memorized every detail of the letter while I talked to D'Arcy. Then when he was not looking, I dropped one of my gloves on the floor under my chair. "The next morning, I stopped at his apartment to look for my glove. While we were talking, we heard people shouting in the street. D'Arcy went to the window and looked out. Quickly, I stepped to the shelf and put the letter in my pocket. Then I replaced it with a letter that looked exactly like it, which I had made it the night before. "The trouble in the street was caused by a man who had almost been run over by a horse and carriage. He was not hurt. And soon the crowd of people went away. When it was over, D'Arcy came away from the window. I said goodbye and left. "The man who almost had an accident was one of my servants . I had paid him to create the incident." Dupin stopped talking to light his pipe. I did not understand. "But, Dupin," I said, "why did you go to the trouble of replacing the letter? Why not just take it and leave?" Dupin smiled. "D'Arcy is a dangerous man," he said. "And he has many loyal servants. If I had taken the letter, I might never have left his apartment alive." What is Dupin probably?
An actor. A professor. An official. A detective.