Dr. Fell mused a while.
"The extraordinary feature about the Depping murder" he rumbled, after refreshing himself with whisky, "is that the thing explained itself, if you only bothered to inquire what the facts meant.
"I had a strong inkling of who the murderer was long before I had met her. The first fact that established itself beyond any question was that the murderer was definitely NOT one of the little community at or around The Grange. And the murderer was not only an outsider, but an outsider who had known Depping in his past (and, at that time) unknown life."
"Why?"
"Let us begin with the attempted murder of Spinelli by Depping, at the point in our previous deductions where we had decided that it was Depping who left the house in disguise and came back to it through the front door. The problem was this: Was Depping working with a confederate whom he had planted in that room as an alibi? Or was he working alone, and X somebody who had come unexpectedly to that room with the intent to kill — only helping him in his deception when X saw the opportunity of an alibi for him (or herself?) In either case, were there any indications as to X's identity?
"Very well. Now, all the weight of evidence lay against Depping's having a confederate, to begin with, why did he NEED a confederate at all? It's a very poor alibi, you know, merely to put somebody in a room; somebody who can't show himself, or act for you, or prove you are there. If Depping had genuinely wanted an alibi for his presence in that room, he would have had a confederate do something that could have testified to his presence… running the type- j writer, for example. Or even moving about or making conspicuous sounds of any sort. But it didn't happen. And what's the good of an alibi that doesn't alibi, but merely puts you into the power of your confederate? Why share a secret that you don't have to share at all?
"Which brings us to the second and most powerful objection. Depping was acting a part before that community. The last thing in the world he would think of doing would be to reveal himself: to tell what he was—"
"Hold on!" interrupted J. R. "I made that objection myself.- He couldn't tell anybody what he'd been, or that he intended to go out and murder Spinelli; he didn't know or trust anybody well enough for that. But somebody" — he sighted over his eyeglasses at Morgan—"invented a long yarn about an 'innocent victim,' who had been persuaded by Depping to stay there on the grounds that he was playing a practical joke on somebody, and afterwards the accomplice couldn't reveal the plot without incriminating himself."
Dr. Fell followed the direction of his glance at Morgan, and chuckled.
"Consider it," he said. "Can any of you conceive of a person from whom an excuse of that sort would come with less plausibility than from Depping? Could any of your community, Morgan, imagine Depping in the role of light and graceful practical joker? If he had come to you with a proposition of that sort, would you have believed him or assisted him?… I doubt it. But the real objection lies in the eight of swords. If you believe in an innocent confederate, what becomes of that symbol and trade-mark of the murderer? How did it come there? Why did an innocent confederate bring it there to begin with?”