Two days passed, and nothing occurred. My watching seemed hopeless, and I resolved to try the effect of a disguised interrogatory. It might help to confirm my already settled conviction, if it did not elicit any new evidence.  
Seated in Bourgonef's room, in the old place, each with a cigar, and chatting as of old on public affairs, I gradually approached the subject of the recent murder.
 
"Is it not strange," I said, "that both these crimes should have happened while we were casually staying in both places?"
 
"Perhaps we are the criminals," he replied, laughing. I shivered slightly at this audacity. He laughed as he spoke, but there was a hard, metallic, and almost defiant tone in his voice which exasperated me.
 
"Perhaps we are," I answered, quietly. He looked full at me; but I was prepared, and my face told nothing. I added, as in explanation, "The crime being apparently contagious, we may have brought the infection from Nuremberg."
 
"Do you believe in that hypothesis of imitation?"
 
"I don't know what to believe. Do you believe in there being only one murderer? It seems such a preposterous idea. We must suppose him, at any rate, to be a maniac."
 
"Not necessarily. Indeed there seems to have been too much artful contrivance in both affairs, not only in the selection of the victims, but in the execution of the schemes. Cunning as maniacs often are they are still maniacs, and betray themselves."
 
"If not a maniac," said I, hoping to pique him, "he must be a man of stupendous and pitiable vanity,—perhaps one of your constant- minded friends, whom you refuse to call bloodthirsty."
 
"Constant-minded, perhaps; but why pitiably vain?"
 
"Why? Because only a diseased atrocity of imagination, stimulating a nature essentially base and weak in its desire to make itself conspicuous, would or could suggest such things. The silly youth who 'fired the Ephesian dome,' the vain idiot who set fire to York Minster, the miserable Frenchmen who have committed murder and suicide with a view of making their exit striking from a world in which their appearance had been contemptible, would all sink into insignificance beside the towering infamy of baseness which—for the mere love of producing an effect on the minds of men, and thus drawing their attention upon him, which otherwise would never have marked him at all—could scheme and execute crimes so horrible and inexcusable. In common charity to human nature, let us suppose the wretch is mad; because otherwise his miserable vanity would be too loathsome." I spoke with warmth and bitterness, which increased as I perceived him wincing under the degradation of my contempt.
 
"If his motive WERE vanity," he said, "no doubt it would be horrible; but may it not have been revenge?"
 
"Revenge!" I exclaimed; "what! on innocent women?"
 
"You assume their innocence."
 
"Good God! do you know anything to the contrary?"
 
"Not I. But as we are conjecturing, I may as well conjecture it to have been the desire to produce a startling effect."
 
"How do you justify your conjecture?"
 
"Simply enough. We have to suppose a motive; let us say it was revenge, and see whether that will furnish a clue."
 
"But it can't. The two victims were wholly unconnected with each other by any intermediate acquaintances, consequently there can have been no common wrong or common enmity in existence to furnish food for vengeance."
 
"That may be so; it may also be that the avenger made them vicarious victims."
 
"How so?"
 
"It is human nature. Did you ever observe a thwarted child striking in its anger the unoffending nurse, destroying its toys to discharge its wrath? Did you ever see a schoolboy, unable to wreak his anger on the bigger boy who has just struck him, turn against the nearest smaller boy and beat him? Did you ever know a schoolmaster, angered by one of the boy's parents, vent his pent-up spleen upon the unoffending class? Did you ever see a subaltern punished because an officer had been reprimanded? These are familiar examples of vicarious vengeance. When the soul is stung to fury, it must solace itself by the discharge of that fury—it must relieve its pain by the sight of pain in others. We are so constituted. We need sympathy above all things. In joy we cannot bear to see others in distress; in distress we see the joy of others with dismal envy which sharpens our pain. That is human nature."
 
"And," I exclaimed, carried away by my indignation, "you suppose that the sight of these two happy girls, beaming with the quiet joy of brides, was torture to some miserable wretch who had lost his bride."
 
I had gone too far. His eyes looked into mine. I read in his that he divined the whole drift of my suspicion—the allusion made to himself. There often passes into a look more than words can venture to express. In that look he read that he was discovered, and I read that he had recognized it. With perfect calmness, but with a metallic ring in his voice which was like the clash of swords, he said:
 
"I did not say that I supposed this; but as we were on the wide field of conjecture—utterly without evidence one way or the other, having no clue either to the man or his motives—I drew from the general principles of human nature a conclusion which was just as plausible—or absurd if you like—as the conclusion that the motive must have been vanity."
 
"As you say, we are utterly without evidence, and conjecture drifts aimlessly from one thing to another. After all, the most plausible explanation is that of a contagion of imitation."
 
I said this in order to cover my previous imprudence. He was not deceived—though for a few moments I fancied he was—but replied:
 
"I am not persuaded of that either. The whole thing is a m............