The doctor shook his head. “I can’t say, since I do not yet know its nature,” he replied. “If it was the same as was employed in Colburn’s case, we can make a rough guess, however. A very small quantity, applied to a scratch in his tongue, caused death in two hours and a half. We may assume that very much larger quantity would be contained in a syringe, and it was driven well into the tissues. Death might well have occurred within a few minutes. But in any case, there would have been time to dispose of the syringe.”

The doctor turned and pointed to the window. “That’s open at the top, as you see, and the curtains do not meet by a couple of feet or more. He could have thrown it out there without the slightest difficulty.”

Whyland turned to the three men, who had been standing by the door. “Slip down below, Waters, and search the pavement and roadway outside this window for a hypodermic syringe,” he said. “Sharp, now! Mr. Ludgrove, come to this window for a moment; you know this street better than I do. That’s your place opposite, isn’t it? What’s behind that window over the shop?”