Caruth threw up his hands. “Very likely,” he groaned. “And yet how could an accomplice know that Wilkins had gotten away with the letter before she knew it herself? For he was probably dead when she did discover it. If not, he must have been killed within a very few seconds afterwards. She made no signal; she had no reason to make any. How could an accomplice know?”
“Let’s see!” Bristow looked around the room. “You were sitting in here, were you not?” he asked.
“Yes.”
“Of course you were. My dear fellow, can’t you really answer your own question?”
Caruth shook his head hopelessly. “I’ve thought and thought,” he declared, “but I don’t progress an inch. Can you answer it?”
“Of course! Look through the sliding doors behind you. What is that thing that cuts across the upper left-hand corner of the window at the back?”
Caruth looked, then rose to his feet. Chagrin was pictured on his features. “Do you know,” he admitted disgustedly, “I never thought of that before? I never realized that that infernal fire-escape crossed my window. There is such a little piece of it that——”
“There is quite enough to permit a man to peer into your rooms. No doubt the murderer was watching there, and when Wilkins tried to escape by that route he found death awaiting him.”
“But—but—how did the spy know that Wilkins had changed the letters?”
“Perhaps he didn’t know it. Perhaps he was a mere thief who killed for money; or perhaps he saw the shift which was made too deftly for you to notice; or perhaps the girl signalled him.”