Exactly when it was first noted that fired bullets from a given weapon possessed a certain number of equally spaced impressed grooves, all inclined in the same direction and at the same angle, and which were the same on every other bullet fired through that weapon, will probably never be known.
Likewise, it will never be known when the next logical step was taken to compare the width, number and degree of inclination of the grooves with those from weapons of a different make.
The next step, however, required a quantum leap in lateral thinking to show that all bullets fired through the same weapon bore microscopic stria (parallel impressed lines) which were unique to the weapon in which they were fired.
Early cases of bullet identification. In June 1900, an article appeared in the Buffalo Medical Journal, by Dr A.L. Hall, to the effect that bullets fired through different makes and types of weapon, of the same calibre, were impressed with rifling marks of varying type. Unfortunately, Dr Hall never expanded on his original article.
In 1907, as a result of riots in Brownsville, Texas, where members of the US infantry opened fire, staff at the Frankfort Arsenal were tasked with identifying
Handbook of Firearms and Ballistics: Second Edition Brian J. Heard © 2008 John Wiley & Sons, Ltd.
which of the weapons were fired. As a method of identification, magnified photographs of the firing pin impressions on the cartridge cases were used. By this means, they were able to positively identify that of the 39 cartridge cases examined; 11 were from one weapon, 8 from a second, 11 from a third and 3 from a fourth. The six remaining cartridge cases were not identified. As to the recovered bullets, the examiners concluded that the bullets bore no distinctive markings as to the particular weapon from which they were fired. The only conclusions reached were that they had, by the rifling characteristics, been fired from either a Krag or a Springfield rifle.
Use of photomicrographs. This epochal work by the staff at Frankfort Arsenal was not recognized for a number of years and it was not until 1912 when Victor Balthazard made the next profound advancement to this science. Balthazard took photomicrographs of bullet lands and grooves in an attempt to identify the weapon from which the bullet was fired. From these examinations, he came to the conclusion that the cutter used in rifling a barrel never leaves exactly the same markings in its successive excursions through a barrel. These markings, which by inference must be unique to that barrel, are then imprinted as a series of striations on any bullet passing through that barrel. He thus reasoned that it is possible to identify, beyond reasonable doubt, that a fired bullet originated from the barrel of a certain weapon and none other. The significance of Balthazard's work cannot be overestimated, for it is upon this premise that the whole of modern science of bullet identification rests.
Balthazard's work, however, extended beyond that of matching striations on bullets and included the markings imprinted on fired cartridge cases in self-loading pistols. The markings he identified as being those bearing identifiable stria and markings unique to a certain weapon were those caused by the firing pin, breech face, cartridge extractor and ejector. He reasoned that the final pass made by a cutting or finishing tool in, for example, the cartridge extractor, left a series of striations which were unique to that extractor. Likewise, the finishing strokes made by a hand-held file, for example, in rounding off the firing pin tip, once again left marks which were unique to that piece of work.
Balthazard's work was, however, exceedingly labour intensive, requiring the production of numerous photomicrographs under exactly the same lighting and magnification. These photomicrographs then had to be painstakingly enlarged under identical conditions to produce the photographs which could be compared to the unaided eye.
In 1923, a paper was published in the Annales de Medicine Legale by De Rechter and Mage which discussed the merits of using firing pin impressions for the identification of the weapon used. Whilst some reference was made in this paper to the work carried out by Balthazard, it did not fully credit him for his work with self-loading pistols.
At about the same time, Pierre Medlinger also mentioned the reproduction of minute irregularities in the breech face on the soft brass of American primers.
The matter was, however, taken no further than that, with no mention of the possibility of identification of the weapon in which it was fired.
Identification of weapon from breech face markings. Whilst it was accepted at this time that it was possible to match a fired bullet and cartridge case with a given weapon, there was no information available to indicate, from fired bullet or cartridge case alone, which make and model of weapon it was fired in. In 1932, Heess, Mezger and Hasslacher rectified this via the publication of an immense amount of data in volume 89 of the Archiv fur Kriminologie entitled 'Determination of the Type of Pistol Employed, from an Examination of Fired Bullets and Shells'. This article was translated and reprinted in the 1932 edition of the American Journal of Police Science. Appended to the paper was an 'atlas' containing photographs of 232 different self-loading pistols each containing an illustration of the breech face and the markings produced on fired cartridge cases. Measurements of width, number, direction and angle of rifling twist were also included. This atlas was produced commercially as a series of cards which were added to on a regular basis. Unfortunately, this has been unavailable for several decades with copies being much sought after as collector's items.
Early use of comparison microscope. It was not, however, until 1925 that mention was first made of a comparison microscope which enabled the simultaneous viewing of magnified images of two bullets or cartridge cases for forensic comparison purposes. Calvin Goddard in a paper published in the 1936 edition of the Chicago Police Journal attributes the development of the comparison microscope to a Philip Gravelle in 1925. This, he states, was a development of the comparison microscope used by Albert Osborn for document examination. The microscope so formed consisted of a Zeiss optical bridge, Spencer microscope bodies, Leitz eyepieces, Bausch and Lomb objectives and bullet mounts constructed by Remington Arms Company.
The optical bridge referred to is a 'Y'-shaped tube, the two arms of which fit over the vertical tubes of two microscopes. By a series of prisms inside the 'Y' tube, the images are directed into a single eyepiece. The resultant image is a circular field of view composed of the image from the left microscope in the left side of the field and that from the right in the right side of the field. The images are separated by a fine line in the centre of the field.
Emile Chamot of Cornell University also describes the use of a comparison microscope, using an optical bridge designed by Bausch and Lomb, for examining small arms primers in 1922. The optical bridge, however, dates back to a Russian mineralogist, A.V. Inostrszeff, who, in 1885, designed an optical bridge for comparing the colour of minerals.
It does not matter who actually invented the comparison microscope, for it was Philip Gravelle who first realized its use in the forensic comparison of stria on bullets and cartridge cases.
Shortly after the 1925 publication of the paper in the Army Ordnance Journal, the Spencer Lens Company manufactured the first commercial comparison microscope. This was very soon followed by Bausch and Lomb, and Leitz.
In 1927, Mr Robert Churchill, the famous English gunmaker, became interested in the comparison microscope. After seeing illustrations of a comparison microscope in an American periodical, he had a similar instrument manufactured for himself.
There is some dispute as to when Churchill first used his comparison microscope, with Mathews (1962) indicating it was in solving the famous Constable Gutteridge murder case. Major Burrard (1934) is convinced, however, that the Gutteridge case was solved by the War Office experts using a simple monocular microscope and photomicrographs.
The brief facts concerning the murder of Constable Gutteridge are as follows. In a motor car, used by the murderers of Constable Gutteridge, was found a fired revolver cartridge case. After many months ' work, the police were convinced that two men, Brown and Kennedy, were the murderers. Two revolvers were found in the possession of Brown, and the whole case hinged on whether one of these was the murder weapon. Eventually, it was established that one of the revolvers did in fact fire the cartridge case and, after trial at court, Brown and Kennedy were hanged for the murder.
Whilst the fact that a microscopic comparison had been made was not particularly significant, this was the first time that such evidence had been presented to a court of law in the United Kingdom.
These early commercial comparison microscopes still consisted of the bottom half of two normal microscopes joined by an optical bridge. In the 1930s, the first real purpose-built microscope appeared in which the objective lenses were attached directly to the optical bridge. This made for a very compact instrument which could be mounted on a single base stand.
Introduction of the binocular comparison microscope. The next major improvement was the introduction of binocular eyepieces. It should be noted here that this did not give stereoscopic images as each stage still only had a single objective lens. It merely made operational use of the instrument much more comfortable.
It is often claimed that two-dimensional (2D) photographic reproductions of striation comparisons do not represent the three-dimensional (3D) views obtained on the microscope. Whilst there is some truth in the statement that photographic representation of striation matches is of little evidential use, this is not due to photographs being only 2D. In fact, the view obtained through the eyepieces is 2D, as the single objective lens system used in comparison microscopes is incapable of representing three dimensions.
Improvements in illumination. Apart from considerable improvements in optical quality, the only other real improvement in comparison microscope design has been the introduction of optical fibre and coaxial illumination.
Obtaining the correct lighting balance to enhance the micro stria under observation is one of the most difficult aspects of comparison microscopy. To achieve this using a conventional focused tungsten bulb system for each stage so that the light intensity, colour temperature and angle of illumination is identical for both is exceedingly difficult. Modern instruments are, however, now supplied with a single source halogen bulb serving two focused, fibre optical arms. Each stage is thus supplied with a light source of exactly the same intensity and exactly the same colour temperature. Being highly manoeuvrable, the fibre optic light sources can be positioned with an accuracy previously unobtainable.
More modern instruments use a form of lighting once called the 'Ultrapak' or coaxial lighting system. Originally, this lighting system was used on Leitz microscopes which were specifically designed for the examination of paint flakes and fibres. In this type of examination, which was usually concerned with colour determination, a shadowless but incident lighting of the object was required. Shadowless lighting required that the light source be vertically over the object being examined, which presents some problems where a microscope is concerned. The problem was solved by introducing the light into the lens barrel around the outside of the lens system. The light was directed down the lens barrel and, via a lens surrounding the objective lens, was focused on the object being examined. As the light source was now coming from around the objective lens, it gave a 360 ° shadowless illumination of the object. The system has now been updated and appears on modern Leitz comparison microscopes giving a brilliantly clear, shadowless light. The stria appear, not as peaks and furrows as with normal incident lighting, but more as a series of ' bar codes ' . Its real use is, however, in the examination of deeply indented firing pin impressions where normal incident lighting would be almost impossible due to the shadows produced. This considerably simplifies the examination and reduces the eye strain of the examiner.
Photography of stria. Whilst most comparison microscopes have some form of photographic system for recording the striation matches, this is only of any real use in toolmark examination. In toolmark examination, the stria are generally on a flat surface and are easily photographed.
With striations on bullets, the stria are on the circumference of a curved surface, and only a small portion of this can be adequately represented in focus on a single photograph. Modern instruments can now be fitted with a closed circuit television (CCTV) and monitor connected to a video recording device. With this, it is possible to record the striation match around the whole of the circumference of a bullet.
In general, the use of comparison photomicrographs in a court of law to illustrate stria comparisons should be discouraged. At best, they are illustrative of a stria match and at worse, they can be totally misleading to a layman jury. A video recording of the whole circumference of a bullet comparison or the various parts of a match on a cartridge case, however, is far more informative for the court and will remove most of the perceived 'mysticism' behind striation comparisons.
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