The first paper in this series [1] described the application of particle analysis to the identification of gunshot residue. In the course of developing this application, gunshot residue was identified in each of several hundred samples collected. In many instances, the nonfiring hand was sampled as a control, or “handblank” samples were taken from persons who had not fired a gun [2]. Some of these many tests were performed “blind,” that is, without prior knowledge by the analyst of the nature of the sample. No false positives were obtained from nonfiring samples. Nevertheless, it was thought that better proof of the uniqueness of gunshot residue particles was required and that an investigation should be made of the possibility that particles in the natural environment or particles produced by man could closely resemble gunshot residue.

Several methods of bulk elemental analysis, such as fiameless atomic absorption, flame emission spectroscopy, neutron activation analysis, and photoluminescence spectroscopy, can reliably and quantitatively determine the amounts of antimony and barium (antimony and lead in the case of photoluminescence) removed from the hand. The information thus furnished, however, in most cases is not sufficient to constitute presumptive evidence of the presence of gunshot residue. Many analyses are inconclusive because the amounts of antimony and barium (lead) are less than certain “thresholds” considered necessary because these elements are not unique to gunshot residue. Firings from .22 caliber weapons, unless the cartridge is known to be a Federal brand, are not usually analyzed because domestic rimfire primers, except Federal, do not contain antimony. Understandably, there has been great interest in alternative analysis methods capable of furnishing additional information of potentially higher specificity for gunshot residue.

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The final step in the development of the particle analysis method for gunshot residue detection was a program of case assistance for law enforcement agencies, carried out during the first nine months of 1977.

Incoherent vacuum ultraviolet (VUV) light has been used to deposit aluminum from photodissociated trimethylaluminum vapor at room temperature. The depositions of aluminum on quartz, silicon, and sapphire show distinct patterns of the shadow mask that was used to shield areas of the substrate from the VUV light beam. Because of its simplicity and low cost, this new method may provide an attractive alternative to presently used methods for depositing metals, semiconductors, and insulators.