“Now, even you, Dr. Priestley, failed to read the riddle of the broken hypodermic needle and the incrustation of potassium carbonate round the puncture. Yet it was ridiculously simple. I secured a piece of metallic potassium, and moulded it into the shape of a bullet to fit an airgun which I possessed. Into the head of this bullet I inserted the broken end of a hypodermic needle, which I had already charged with the same drug as had been so effectual in the case of Mr. Colburn. Keeping this prepared bullet in paraffin, to avoid oxidation, I placed the airgun ready upstairs, and waited for Mr. Copperdock’s return from the Cambridge Arms. He brought two friends home with him, and I was afraid at first that I should be compelled to postpone my attempt. It was essential to my scheme that he should be alone in the house when I fired the gun.