"You will see," my friend went on, "that I have tried to answer another question. Not just 'How did the murderer get out of the room?', but also 'How did he get into it?' He used the same window both ways, I think."

"So far, then, the picture is like this. We have a murderer with a peculiar voice, and who is unusually agile. We have a murder without motive, a murder that is brutal and horrible even for the worst kind of criminal. How many murderers kill with their own hands, and then push the body, head downwards, up a chimney? And how strong our murderer is! He pushed the body up alone, but it took three or four people to pull it down. And think of those handfuls of long grey hair on the floor. Have you ever tried to pull hair out of someone's head? You need to be very strong to do that. You also need to be strong to cut right through someone's neck -- with just a razor. And why did the old lady have so many broken bones? Because the murderer pushed her body through the open window, and it fell down onto the stones of the yard below."

"But now, let's look again at the room. You remember that on the floor there were two bags of gold, which Adolphe Le Bon carried to the house three days before. The police are so excited by this! Nearly four thousand francs in gold! Here, they say, is the motive for the murder. Well, four thousand francs in gold is a lot of money, and is certainly a possible motive for murder. But remember, my friend, the gold was not taken -- it was still there, on the floor. So what kind of thief is that? A very, very stupid one, a thief who murders two women and then when he leaves, forgets to take the gold with him! No, no, we must forget the gold. It was not the motive for these murders."

I felt a little ill when Dupin asked me this question. I shook my head. "A madman," I said, "has done this -- a wild and horrible madman, who has escaped from some hospital somewhere."

"One more thing to finish the picture. Remember what the room looked like-broken chairs and tables everywhere, the mattress on the floor, nothing in its place. Now, surely, our picture is finished. What kind of murderer is so unusually strong, so unusually agile, has so peculiar a voice, kills in so brutal and horrible a way, without motive? Tell me, what is the answer?"

Dupin put his hand in his pocket and took something out. He put it on his hand and held it out to me. It was some short, orangey-brown hair.

"That is a possible answer, certainly," Dupin replied. "But even madmen do not have as peculiar a voice as the one heard on the stairs. Madmen speak a language of some kind. Perhaps they say strange things, but at least they speak in words. Now, there is one more thing…"

"I took this from between the fingers of Madame L'Espanaye's hand," he said. "What do you make of it?"

"Dupin!" I said, astonished and afraid. "This hair is most unusual. It is not human hair!"

"Did I say it was?" Dupin said. He put the hair back into his pocket, and then showed me a piece of paper. "You remember the marks on the neck of Mademoiselle L'Espanaye -- marks made by the fingers that killed her? Here is a drawing of those marks, just as they were on the neck. Now, please put your hand on the paper, with all your fingers in the same places as the marks."

"These marks," I said, "were not made by a human hand."

I tried to do this, but could not. I don't have small hands, but my fingers were much shorter and my hand much narrower than the marks on the drawing.

The page described an animal that is found in the East Indian Islands -- the orang-outang. It is a very large animal, bigger than a man, and is strong, agile, clever, and very, very dangerous. At once I understood just how horrible these murders were.

Dupin stood up and went to get a book from the table behind him. He brought the book to me.

"I want you to read this page," he said.

"Your drawing of the marks made by the fingers," I said, "is just as the book describes the orang-outang's hand. Also, the book describes its orangey-brown hair, which sounds just like the hair you showed me. But I still can't understand this terrible mystery. People heard two voices arguing -- and the other voice was the voice of a Frenchman. Everybody agreed about that."

"True," said Dupin. "And you will remember two of the words they heard -- Mon Dieu. When do we say this? When we are angry, afraid, surprised, unhappy… I have thought about these words and made a little picture of this Frenchman, which will answer all the questions in this mystery. This is my picture. A Frenchman brings home an orang-outang from the East Indian Islands, but one night the animal escapes from him. Our Frenchman follows it through the city, trying to catch it. When the orang-outang gets into the house in the Rue Morgue, the Frenchman sees what happens, but cannot catch the animal or stop it killing the two women."

"Is this picture a true one? Of course, I don't know. But if I am right, the Frenchman himself is innocent of these murders. And if he is innocent, perhaps he will answer my advertisement. I left it at the office of Le Monde newspaper on our way home last night."

"I do not know it," said Dupin. "I am not sure of it. But I found this small piece of ribbon on the ground at the bottom of the lightning-rod. Look."

Dupin gave me a piece of paper, and I read this:

CAUGHT IN THE BOIS DE BOULOGNE, early in the morning of the 4th of June, a large orang-outang, probably from the East Indian Islands. The owner, who is a sailor on a Maltese ship, can have the animal back if he comes to the following address in the Faubourg St. Germain…

He gave me the ribbon to look at. It was a dark-red colour, and old and dirty.

"Sailors always use ribbons like these," Dupin said, "to tie back their long hair. And this colour is a favourite of Maltese sailors. You see, if I am right about this, it will make the man think carefully."

"But will he answer the advertisement?" I said. "He saw the terrible things that his orang-outang did. Won't he be afraid to say he is its owner?"

Once again, I was astonished by what Dupin knew. "How could you possibly know," I asked, "that the man was a sailor, and that he belonged to a Maltese ship?"

"Yes, he will he a little afraid," said Dupin. "But I hope that he will think like this, and will say to himself: I am innocent. I am poor. I can sell my orang-outang for a lot of money, and I don't want to lose that money. What danger am I in? They found the animal in the Bois de Boulogne -- a long way from that house in the Rue Morgue. Who will ever know that the orang-outang did those murders? Or that I saw what happened? The police know nothing. But this advertiser knows something about me. If he wants to, he can find me easily. If I don't answer the advertisement, perhaps he will think that I have something to hide. He will start asking questions, about the animal, or about me, perhaps. No, it's better for me to answer the advertisement, get the orang-outang back, and keep the animal hidden away for a time."

At the very moment when Dupin stopped speaking, we heard the sound of feet on the stairs.