"I can now say definitely that Mr. Miller was shot with the muzzle somewhere between twelve and fifteen inches from his temple. I still do not understand why the killer approached so close without--" "Morris Miller was almost stone deaf," interrupted Brasher. "Ah, that accounts for it; that clears up something that puzzled me." "Since you three have conspired to make me take an interest in crime," his glance swept Jimmy, Matthews, and McCall, "I have gone rather exhaustively into matters that hitherto only interested me casually. I spent two months in the Scientific Crime Detection Laboratory of Northwestern University. Among the subjects I took up were powder marks. "It was obvious to me at the first glance at the wound that it was not self-inflicted. I felt reasonably certain that the weapon was held a greater distance from the head than it would be held if the victim contemplated suicide. That is why I suggested the possibility that he had held the weapon and it had gone off by accident. That seemed a remote possibility, but still a possibility. "Powder marks tell quite an interesting story to the student. Black powder will not leave the same marks at the same distance, either in kind or degree, as will smokeless powder. The same kind of powder fired from a weapon with a short barrel will leave burns that differ radically from those fired from a long barrel. The amount of powder also will make a difference. "Black powder is merely a physical mixture of three ingredients. The charcoal which goes into its composition is not burned at the time of firing and remains unchanged. Each little unburned charcoal grain becomes a secondary projectile, which leaves its mark not only on the surface that received the bullet if it is close enough, but also makes little pits on the base of the bullet. "Smokeless or semi-smokeless powder is a chemical compound in which the ingredients are radically changed in form. At the time of firing, smokeless powder is practically all burned and only gases are left, leaving neither soot nor pits on, the base of the bullet. Smokeless powders will also leave burns on the surface at which the bullet is fired, but neither as black, nor deep, nor as numerous as those left by black powder. "Thus you see, given the same ammunition, the same weapon, it can be ascertained by tests, with a fair degree of accuracy, at what distance a shot was fired. The zone of black around the wound itself, the size of powder marks, the thinness with which they are scattered, all tell their story." "Is this true, Professor, at distances beyond which there are powder marks?" asked Jimmy. "Yes, it is, but not within inches, of course, nor within a few feet, perhaps. But even at those distances it can often be approximated.