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(Testimony of Robert A. Frazier)
Mr. Frazier.
Because the marks which are placed on any belt face are accidental in nature. That is, they are not placed there intentionally in the first place. They are residual to some machining operation, such as a milling ma chine, in which each cutter of the milling tool cuts away a portion of the metal; then the next tooth comes along and cuts away a little more, and so on, until the final surface bears the combination of the various teeth of the milling cutter. In following that operation, then, the surface is additionally scratched-- until you have numerous--we call them microscopic characteristics, a characteristic being a mark which is peculiar to a certain place on the bolt face, and of a certain shape, it is of a certain size, it has a certain contour, it may be just a little dimple in the metal, or a spot of rust at one time on the face of the bolt, or have occurred from some accidental means such as dropping the bolt, or repeated use having flattened or smoothed off the surface of the metal.
Mr. Eisenberg.
Why doesn't a series of the same machines, or repeated use of the same machines, cause the same results, apart from future accidental markings?
Mr. Frazier.
In some instances a certain type of cutter will duplicate a certain pattern of marks. In general you will find for a milling cutter a circular mark. And you may find the same pattern of circles. But that milling cutter does not actually cut the steel; it tears it out, it chips it out, and the surface of the metal then is rough even though the circle is there, the circle is not a smooth circle, but it is a result of tearing out the metal, and you will have a very rough surface. When magnified sufficiently, you can detect the difference even between two similarly milled surfaces because of the minor variations in the cutting operation.
Mr. Eisenberg.
Have you had occasion to examine such similarly-milled surfaces?
Mr. Frazier.
Oh, yes; many times.
Mr. Eisenberg.
Would you go into detail on that?
Mr. Frazier.
Well, part of my work in the laboratory is dealing with tool-marks of all types, from drills, mills, files, cutting instruments, and so on. And when you are dealing with filing marks or milling marks and so on, it is some times possible to identify a particular mill as having made a certain mark on the basis of the grinding marks on that particular mill. But such as a case like this, where the cutting marks have now been altered through use of the weapon and corrosion, or in wear or in filing, some of the original marks are removed, and other marks are in their place, until eventually you reach a condition where that bolt face will be entirely different from any other bolt face. It is a matter actually--when you get down to the basis of it, it is a matter of a mathematical impossibility in the realm of human experience for any two things to ever be exactly alike.
Mr. Eisenberg.
That is because the original markings will not be exactly alike, and then you have added accidental markings on top of the original ones?
Mr. Frazier.
That is right; yes, sir.
Mr. Eisenberg.
Returning for a moment to the original markings, as I under stand it, you have worked with the tools themselves and the impressions the tools themselves leave, as opposed to a tooled surface, such as this.
Mr. Frazier.
I have worked with beth. In other words, in comparing tool-marks, you examine not only the tool, but the marks they produce.
Mr. Eisenberg.
And in working with these tools, as I understand your testimony, you have found that the markings which a tool leaves, which the same tool leaves, will be distinctive.
Mr. Frazier.
That is true, yes. When it is a scrape or an impression from its surface, or something of that nature, it can be very readily identified. But if it is a drill or something of that nature, where you have a tearing operation, then it is not readily identified, but it occasionally can be identified.
Mr. Eisenberg.
Well, how many such examinations do you think you have made?
Mr. Frazier.
Thousands of them.
Mr. Eisenberg.
Have you noticed whether the marks left by a given tool--that you have examined--change over the course of the use of the tool?
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