Sample Collection

Some form of kit containing sampling materials is normally prepared (commercially, or by police forces, or by forensic laboratories) for the purpose of sampling suspects for FDR.180-182

Kit design considerations include (a) avoiding contamination from external sources and cross contamination between sampling areas, (b) lifting efficiency, (c) matrix compatibility with subsequent laboratory procedures, (d) ease of use and preparation, and (e) cost, purity, availability of materials.

Hand sampling methods include:

Cloth

Cotton wool and dilute acid Filter paper

Swabbing

Dilute acid wash

Washing

Paraffin "glove" Film forming polymers

Film Lifts

Adhesive tape

Adhesive Lifts

Adhesive stubs

The analytical technique used strongly influences the type of sampling procedure. Sampling methods fall into two categories: destructive or nondestructive, depending on the effect of the sampling procedure on individual FDR particles, acids tending the break down the particles.

Whatever form of kit is used the lifting efficiency depends to a large extent on the care taken by the sampler.

references

170. G. M. Wolten, R. S. Nesbitt, A. R. Calloway, G. L. Lopel, and P. F. Jones, "Final Report on Particle Analysis for Gunshot Residue Detection," The Aerospace Corporation, El Segundo, CA. Aerospace report no. ATR-77 (7915)-3 (September 1977), 13.

171. G. M. Wolten, and R. S. Nesbitt, "On the Mechanism of Gunshot Residue Particle Formation," Journal of Forensic Sciences 25, no. 3 (July 1980): 533.

172. M. A. Purcell, "Radiotracer Studies of Test-Fired Bullets" (master's thesis, University of California, Irvine, 1976).

173. Wolten and Nesbitt, "On the Mechanism of Gunshot Residue Particle Formation," 533.

174. Wolton et al., "Final Report on Particle Analysis for Gunshot Residue Detection," 46.

175. G. M. Wolten, "Cooperative Gunshot Residue Study," Newsletter no. 2 (March 31, 1976).

176. R. Cornelis, and J. Timperman, "Gunfiring Detection Method Based on Sb, Ba, lead, and Hg Deposits on Hands. Evaluation for the Credibility of the Test," Medicine, Science, and the Law 14, no. 2 (April 1974): 98.

177. J. W. Kilty, "Activity after Shooting and Its Effect on the Retention of Primer Residue," Journal of Forensic Sciences 20, no. 2 (1975): 219.

178. R. S. Nesbitt, J. E. Wessel, G. M. Wolten, and P. F. Jones, "Evaluation of a Photoluminescence Technique for the Detection of Gunshot Residue," Journal of Forensic Sciences 21, no. 3 (1976): 595.

179. R. Cornelis, and J. Timperman, "Gunfiring Detection Method Based on Sb, Ba, Pb, and Hg Deposits on Hands. Evaluation for the Credibility of the Test, Medicine, Science, and the Law 14, no. 2 (April 1974): 98.

180. J. A. Goleb, and C. R. Midkiff, Jr., "Firearms Discharge Residue Sample Collection Techniques," Journal of Forensic Sciences 20, no. 4 (1975): 701.

181. M. Tassa, N. Adan, N. Zeldes, and Y. Leist, "A Field Kit for Sampling Gunshot Residue Particles," Journal of Forensic Sciences 27, no. 3 (1982): 671.

182. K. K. S. Pillay, W. A. Jester, and H. A. Fox III, "New Method for the Collection and Analysis of Gunshot Residues as Forensic Evidence," Journal of Forensic Sciences 19, no. 4 (1974): 768.

Experimental

Objectives, Sampling Procedures, Instrumentation, and Conditions

The purpose of the experimental work was to improve systems for FDR detection and identification, with particular reference to the Northern Ireland situation. This involved looking at all aspects including suspect handling, sampling procedures, laboratory preparation, analysis techniques, interpretation, and presentation of results in a court of law. There is very little information in the literature about suspect handling, contamination avoidance, interpretation of results, and presentation of evidence in court. By taking an overview and a practical approach to all aspects of the system, it is hoped that by introducing improvements, however minor, in each area, these will have a cumulative effect, leading to a substantial overall improvement. This is a novel approach, the vast majority of the literature dealing with scientific methods of sampling, detection, and identification, which while extremely important is not the end product; the end product is the value and credibility of evidence given in court. The main areas for consideration were as follows.

At the start of 1978 the particle analysis method183 replaced the flameless atomic absorption bulk elemental method184 as the firearm residue detection method in the NIFSL. Since then the particle analysis method has been substantially improved by the use of a sample concentration/cleanup procedure,185 the addition of a backscattered electron detector, and the development of an automated residue detection system.186,187 Despite these improvements the technique remains costly and labor intensive. Certain aspects of the system required further work, in particular, the particle classification scheme: discharge particles from mercury fulminate-primed ammunition and discharge particles from new primer types (Sintox).

The validity of the particle classification scheme was tested by examining items that may produce similar particles, paying particular attention to blank cartridges, the main uses of which that are likely to be encountered in casework are cartridge tools and blank firing replica/imitation firearms.

The particle classification scheme is based on modern primed ammunition and consequently mercury fulminate-primed ammunition is not included. Mercury-containing particles from the discharge of mercury fulminate-primed ammunition are rarely detected in casework. Discharge residue from such ammunition was tested in an effort to provide an explanation for this. Discharge particles from Sintox-primed ammunition was also examined with a view to anticipating future problems the criminal use of

this new ammunition may cause for the particle analysis method, range of fire estimations, and the identification of bullet holes.

A major review of 23 years of casework data was undertaken for the following reasons:

To check the validity of the literature review on the chemistry of ammunition, much of which is based on information gathered over a 23-year period from numerous sources, many of which are of a nonscientific nature, for example, gun magazines, newspaper articles, manufacturers' sales literature.

To demonstrate the variations in and complexity of the basic item involved in firearms crimes, the round of ammunition, a detailed knowledge of which can aid both the physical and chemical investigation of scenes of crime and the subsequent laboratory examination.

To record information gained from a terrorist campaign lasting 26 years, some of which will be of interest and benefit to the scientific community and will not be found published elsewhere.

To clarify the list of accompanying elements in the particle classification scheme and the levels at which they are found.

To provide an insight into the types of mercury-containing particles detected in casework.

With the emphasis on quality all systems were explored, both internal and external, with a view to ensuring that they could withstand close scrutiny from any source, that the possibility of cross contamination of suspects with explosives and/or firearm discharge residue is minimized, and that contamination risks within the laboratory are identified and minimized or eliminated.

The detection and identification of the organic constituents in FDR has the potential to be used either as a screening technique or, much more likely, as a complementary technique to the particle analysis method. The particle analysis method has proved very satisfactory and has been well tried and tested in casework and court. The objective is to devise an efficient system for organic firearm residue detection that is entirely compatible with the particle analysis method. As a suspect may need to be examined for both firearm and explosive residue the method must also be compatible with organic explosive residue detection techniques.

Summary of aims:

Improve the particle classification scheme.

Explain the scarcity of discharge particles containing mercury.

Clarify the types of discharge particles containing mercury that have been detected in casework.

Gain information about Sintox ammunition in anticipation of its use in crime.

Increase knowledge about the chemistry of firearms by reviewing 23 years of casework results and related laboratory tests.

Improve suspect processing procedures and contamination avoidance measures.

Devise a method to enable organic FDR detection to be readily incorporated into our existing systems for inorganic FDR and organic explosive residue detection.

Substantially improve the overall system for firearm and explosive residue detection from the initial arrest of the suspect to the presentation of evidence in court.

Note: For convenience the elements lead, antimony, and barium are referred to as the primary elements in FDR particles. Thus, a single primary element particle would be termed lead only, antimony only, or barium only but it could have, and typically does have, other elements present in the particle from the list of permitted additional accompanying elements.

The terms major, minor, and trace level are defined below and when recording the analysis of a particle all the elements present at a particular level are listed in order of descending peak height. The terms major, minor, and trace are defined in terms of peak height rather than concentration. The strongest peak height should be "on scale" and background levels must be allowed for. The peak heights depend on sample surface irregularities and matrix effects and there is a further complication with overlapping peaks. With this in mind the terms are defined as follows:

Major: Any element whose main peak height is greater than 1/3 of the peak height of the strongest peak in the spectrum.

Minor: Any element whose main peak height is between 1/10 and 1/3 of the peak height of the strongest peak in the spectrum.

Trace: Any element whose main peak height is less than 1/10 of the peak height of the strongest peak in the spectrum.

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