“You mean Thurlow Potts is not our man?” cried the Inspector. “But that can’t be, Ellery. He admitted it. You heard him admit the killings!”
“No, no, that’s not it,” muttered Ellery. “Thurlow did commit those murders — it was his hand that took the lives of Bob and Mac Potts.”
“Then what do you mean?”
“There’s someone else, Dad. Someone behind Thurlow.”
“Behind Thurlow?” repeated his father stupidly.
“Yes, Dad. Thurlow was merely the hand. Thurlow pulled the triggers. But he pulled them at the dictation, and according to the plan, of a brain, a boss — the real murderer!”
Major Gotch retreated into a corner of the chapel, like a cautious bear, and it was curious that thenceforth he kept his old puff eyes fixed upon the pale blinking eyes of his crony, Stephen Brent.
“Let me analyze this dreary, distressing business aloud,” continued Ellery wearily. “I’ll work it out step by step, Dad, as I see it now. If I’m wrong, call Bellevue. If I’m right—” He avoided looking at the others. Throughout most of what followed, he kept addressing his father, as if they had been alone with only the quiet walls of the chapel to keep them company.
“Remember how I proved the Old Woman’s signature on that typewritten confession we found on her body was a forgery? I placed the stock memorandum against a windowpane; I placed the confession over the stock memorandum; and I worked the confession about on the memo until the signature of the one lay directly over the signature of the other. Like this.” Ellery went to a clear sunny window of the chapel and with the two documents illustrated his thesis.
“Since both signatures were identical in every curve and line,” he went on, “I concluded — and correctly — that one of the signatures had been traced off the other. No one ever writes his name exactly the same way twice.”
“Well?” The Inspector was inching toward the chapel door.
“Now since the stock memo was handed to Charley Paxton in our presence by the Old Woman herself — in fact, we saw her sign it — we had every right to assume that the signature on the memorandum was genuine, and that therefore the signature on the confession had been traced from it and was the forgery.
“But see how blind I was.” Ellery rapped the knuckles of his free hand against the superimposed documents his other hand held plastered against the window. “When a signature is traced off by using light through a windowpane, in what position must the genuine signature be in relation to the one that’s to be traced from it?”
“You’ve got to put the document being forged above the genuine signature, of course,” replied the Inspector. He was looking around, restlessly.
“Or in other words, first you lay down on the window-pane the genuine signature, then you place the document to be forged over it. Or to put it still another way, it’s the genuine document that lies against the glass, and the fake document that lies against the genuine one. Therefore,” said Ellery, stepping back from the window, “if the signature on the confession was the traced one, as we believed, then the confession must have been lying upon the stock memo, and the stock memo must have been lying against the windowpane. Is that clear so far?”
“Sure. But what of it?”
“Just a minute, Dad. Now, all the Old Woman’s signatures were written with a heavy, soft leaded pencil.” The Inspector looked puzzled by this irrelevance.
“Such pencils leave impressions so thick and soft that when they are pressed on and written over, as would have to be done in the tracing of a signature written by one of them, they necessarily act like a sheet of carbon paper. That is, when two sheets are pressed together, one on top of the other, and a soft-pencil signature on the bottom sheet is traced onto the top sheet, the very act of tracing, the very pressure exerted by the tracing agent, will produce a faint pencil impression on the back of the top sheet, because it’s that back surface on the top sheet which is in direct contact with the soft lead of the original signature on the bottom sheet. Is that clear?”
“Go on.”
“I’ve already shown that, in order to have been a forgery, the confession must have been the top sheet of the two. But if the confession was the top sheet, there should be a faint pencil impression of Cornelia Potts’s signature (in reverse, of course, as if seen in a mirror) on the back of the confession sheet.”
“Is there?”
Ellery walked over to his father, who by this time was standing, alert, against the chapel door. “Look Dad.”
The Inspector looked, quickly. The reverse side of the confession was clean, without smudge.
“That’s what I saw a few moments ago, for the first time. There is not the slightest trace of a pencil mark on the back of this confession. Of course, there could have been such an impression and for some reason it might have been erased; but if you examine the surface sheet carefully, you’ll find no signs of erasure, either. On the other hand, look at the back of the stock memorandum! Here” — Ellery held it up — “here is the clear, if light, impression of the signature ‘Cornelia Potts’ on the back of the memo, in reverse. And if you’ll hold it up to the light, Dad, you’ll see — as I saw — that the reverse impression of the signature lies directly behind the signature on the face of the memo, proving that the impression was made at the same time as the forgery.
“What does all this mean?” Ellery tapped the stock memorandum sharply. “It means that the stock memo was the top sheet of the two employed in the forgery. It means that the confession was the bottom sheet, lying flat against the windowpane.
“But if the confession was the bottom sheet, then it was the signature on the confession which was being used as a guide and it was the signature on the stock memo which was traced from it!
“But if the signature on the confession was being used as a guide then that signature was the genuine one, and the one on the stock memo was the forgery. Or, to put it in a capsule,” said Mr. Queen grimly, “the Old Woman’s confession was not a forgery as we believed, but was actually written and signed by her own hand.”
“But El,” spluttered the Inspector, “that would make the Old Woman the killer in this case!”
“One would think so,” said his son. “But strangely enough, while Cornelia Potts actually wrote that confession of guilt, and signed it, she did not murder her two sons, nor could she have been the person behind Thurlow who used Thurlow as a tool in the commission of the murders.”
“How can you know that?” asked the Inspector in despair.
“For one thing, Dad, we now know that there never was a substitution of bullets in that first Colt .25 — we know that there was a substitution of guns. Yet in her confession the Old Woman wrote—” Ellery consulted the confession hastily — “the following: ‘It was I who substituted a lethal bullet for the blank cartridge the police had put into Thurlow’s weapon.’ But no bullet was substituted! In other words, the Old Woman thought the same thing we thought at the time — that a substitution of bullets had been made. So she didn’t even know how the first murder was really committed! How, then, could she have been in any way involved in it?
“And look at this.” Ellery waved the confession again. “‘Later it was I who stole one of Thurlow’s other guns and hid it from the police and went with it into my son Maclyn’s bedroom in the middle of the night and shot him with it,’ and so on. Stop and think, Dad: Cornelia Potts couldn’t have done that, either! Dr. Innis told me, just before he left the Old Woman’s bedside that night — shortly before Mac was shot to death — that he had given the Old Woman a sedative by hypodermic injection which would keep her asleep all night.