FREQUENCY OF OCCURRENCE OF CERTAIN CHEMICAL CLASSES OF GSR FROM VARIOUS AMMUNITION TYPES

Transcription

1 FREQUENCY OF OCCURRENCE OF CERTAIN CHEMICAL CLASSES OF GSR FROM VARIOUS AMMUNITION TYPES Zuzanna BRO EK-MUCHA, Grzegorz ZADORA, 2 Insttute of Forensc Research, Cracow, Poland 2 Faculty of Chemstry, Jagellonan Unversty, Cracow, Poland ABSTRACT: The subject of the presented study were thrteen samples of prmer resdues orgnatng from sx types of ammunton, collected from shooters hands mmedately after shootng. The entre area of adhesve tabs wth the secured materal was examned wth the use of SEM-EDX method n the automatc manner. Frequences of occurrence of partcles assgned to varous chemcal classes were calculated for each of the shootng experment performed. In order to fnd out what knd of mutual relatonshps would reveal samples of gunshot resdues collected from varous types of ammunton as well as from the same type of ammunton cluster analyss was appled. The performed cluster analyss showed a promsng tendency of groupng ammuntons accordng to ther types. Moreover, t was checked that a sample of GSR from Makarov 9 mm ammunton, wth some chemcal classes weakly represented, may be correctly classfed nto the approprate group of samples of GSR orgnatng from ths ammunton. KEY WORDS: Gunshot resdues (GSR); SEM-EDX automatc search; Frequency of occurrence of prmer resdues; Multvarate statstcal methods; Cluster analyss. Problems of Forensc Scences, vol. XLVI, 200, Receved 7 November 2000; accepted 5 September 200 INTRODUCTION Physcal and chemcal nvestgatons of frearm dscharge resdues are performed for a number of purposes: dentfcaton of gunshot wounds/damages (establshng the entrance and the ext), estmaton of shootng dstance, dstrbuton of GSR at a crme scene, estmaton of the tme snce dscharge of a frearm, establshng, whether a person has fred a gun, etc. Fulfllng these tasks s always very helpful for reconstructon of an nvestgated crme. However, new challenges for GSR examners arse, as wth a growng frequency the admnstraton of justce asks about the type of am-

2 282 Z. Bro ek-mucha, G. Zadora munton, and so the frearm, used n cases when the only evdence accessble for examnatons are GSR. Thus, to the above lst one more task should be added,.e. the dentfcaton of an ammunton from GSR detected. One of the attempts to solve ths problem s consderaton of the qualtatve dfference n the elemental composton of partcles,.e. searchng for sgnature elements (R. Keeley London Metropoltan Laboratory, The Forensc Scence Servce; prvate nformaton). Another approach s a systematc study of GSR orgnatng from varous ammunton types and usng statstcal and chemometrc methods for evaluaton of the analytcal data, presented by Newoehner [4] and Bro ek-mucha [, 3]. These works, performed for sngle examples of guns and ammuntons so far, revealed the possblty of group dentfcaton of the studed ammunton types. Moreover, t was found that prmer resdues collected wthn a number of experments performed for the same ammunton,.e. Makarov 9 mm, occur wth smlar frequences wthn the approprate chemcal classes, and so the results are repeatable [2]. The am of the presented work was to fnd out what knd of relatons would reveal samples of gunshot resdues collected from varous types of ammunton (wth a number of repettons carred out for selected ammuntons). For the evaluaton of possble dfferences and/or smlartes of the analytcal data, expressed as frequences of occurrence of certan chemcal classes n the entre populaton of the GSR detected n a sample, cluster analyss was appled. EXPERIMENTAL The subject of the presented study was 3 samples of prmer resdues orgnatng from 6 types of pstol ammunton, collected from shooters hands mmedately after shootng three tmes (Table I). TABLE I. THE LIST OF PISTOLS AND THE APPROPRIATE AMMUNITION USED TO OB- TAIN GUNSHOT RESIDUES Pstol Ammunton Number of experments Notaton Brownng 900 Brownng 7.65 mm 3 B Brownng 906 Brownng 6.35 mm b Beretta Luger 9 mm 3 L P-64 & P-83 Makarov 9 mm 4 M Margoln sportng 5.6 mm S TT mm T

3 Frequency of occurrence of certan chemcal classes of GSR from varous ammunton types 283 The whole area of adhesve tabs wth the secured materal was examned wth the use of scannng electron mcroscopy and energy dspersve X-ray spectrometry (SEM-EDX) method n the automatc manner n the same condtons, presented n Table II. The obtaned results were manually checked and corrected. TABLE II. THE EQUIPMENT AND THE ANALYTICAL CONDITIONS OF THE MEASURE- MENTS Scannng electron mcroscope EDX Spectrometer Automatc Search Magnfcaton Acceleratng voltage Workng dstance Acquston tme for sngle partcle Sze of the scanned frame: heght wdth area JSM-5800, Jeol, Japan Lnk ISIS 300, Oxford Instruments Ltd. GunShot, Oxford Instruments Ltd. 200 x 20 kv 0 mm 5 s 54 mm 658 mm mm 2 RESULTS AND DISCUSSION Prmer resdues contanng a combnaton of lead, antmony and barum were taken nto account. The number of partcles representng these chemcal classes was counted for each sample. Examples of obtaned n such a manner results are presented n Table III. As the total numbers of partcles observed for varous samples were dfferent, frequences of occurrence of partcles assgned to partcular chemcal classes were calculated accordng to the followng formula: f = n N = N, {} where: N number of partcles of -th chemcal class; n number of chemcal classes of partcles. In order to compare the data sets obtaned for partcular samples, each of them was taken as a pont n a multdmensonal space where the co-ordnates were frequences of occurrence of 7 chemcal classes of partcles. Thus, a measure of the dfferences between two sets of data, e.g. sample A and B can be the dstance defned n the followng manner:

4 284 Z. Bro ek-mucha, G. Zadora where: d = W f f W AB = n = n = A B, {2} ra rb + ; {3} ra r B + n r A a rank of -th chemcal class n sample A; r A a rank of -th chemcal class n sample B. TABLE III. SELECTED EXAMPLES OF THE RESULTS OF GSR SEARCH Ammunton Chemcal classes of GSR B L2 M4 PbSbBa SbBa 22 2 PbSb PbBa Pb Sb Ba Total For evaluaton the dstances among the studed samples cluster analyss was performed. As the clusterng method, further neghbourhood was appled. Results of the cluster analyss are presented n Fgure. One can observe n the dendrogram that four clusters are present. One of the clusters contans all of the studed samples of GSR obtaned wth Brownng 900 pstol and Brownng 7.65 mm ammunton (B, B2, B3) and solely them. The largest dstance observed wthn ths homogenous cluster was assumed as a formal border above whch samples belong to separate clusters. Another cluster was created by all of the examned samples of GSR obtaned wth P-64 and P-83 pstols and Makarov 9 mm ammunton and one sample obtaned wth Beretta pstol and Luger 9 mm ammunton. Both remanng Luger samples are placed n a cluster together wth the sample obtaned wth TT-33 pstol and the approprate ammunton cal mm. The last cluster conssts of two samples orgnatng from Brownng 906, Brownng 6.35 mm and Margoln, 5.6 mm, thus from ammunton of the smallest calbre. The performed cluster analyss showed a promsng tendency of groupng ammuntons accordng to ther types. Thus, t was worthwhle to check how ths approach works n the case of an unknown sample X. For ths purpose a sample was chosen that was an evdence n a real case examned n the Insttute of Forensc Research, Cracow (Table IV). Ths sample resem-

5 Frequency of occurrence of certan chemcal classes of GSR from varous ammunton types 285 bled these routnely studed materals,.e. wth not all chemcal classes represented, usually wth the unque partcles absent. The results of the cluster analyss performed for all the expermental data, together wth these of sample X, are presented n Fgure 2. One can observe that ths sample s placed wthn Makarov 9 mm cluster. Indeed that was a sample orgnatng from the use of P-64 and Makarov 9 mm ammunton. In Table IV the numbers of partcles of the consdered chemcal classes together wth the approprate frequences of occurrence and ranks are lsted for both, sample X and the most smlar to t sample M3 for comparson. Although n X sample some of the consdered chemcal classes were weakly represented, t was correctly classfed nto the group of data obtaned for other samples of GSR orgnatng from Makarov 9 mm ammunton. TABLE IV. DATA FOR SAMPLE X IN COMPARISON TO SAMPLE M3 Chemcal classes of GSR X Ammunton M3 N f r N f r PbSbBa SbBa PbSb PbBa Pb Sb Fg.. Results of the cluster analyss for the expermental data.

6 286 Z. Bro ek-mucha, G. Zadora Dstance M M2 L X M3 M4 b S L2 T L3 B B2 B3 Fg. 2. Results of the cluster analyss for the data ncludng these from the experments performed and from sample X. Ba CONCLUSIONS Frequences of occurrence of prmer resdues of varous chemcal classes are easy to obtan from the analytcal results of GSR search and can provde an addtonal feature charactersng an ammunton. The performed cluster analyss utlsng ths features showed a promsng tendency of groupng ammuntons accordng to ther types. Thus, t can contrbute to at lest a group dentfcaton of an ammunton n cases when the only accessble for nvestgatons evdence are gunshot resdues collected at a crme scene. In order to elaborate a relable ammunton classfcaton scheme however, an extensve checkng of the repeatablty of the analytcal results for each consdered ammunton s requred. Also, addtonal nformaton mght be necessary to be ncluded for a more precse dfferentaton, e.g., from nspecton nto the nternal structure of prmer resdues by means of the fo-

7 Frequency of occurrence of certan chemcal classes of GSR from varous ammunton types 287 cused on beam spectrometry [5] or on the chemcal composton of other types of resdues (orgnatng from the projectle, case and propellant). Acknowledgement: The authors are grateful to senor commssar Krzysztof Snopkowsk from the Forensc Research Department, the Regonal Headquarters of the Polce, Cracow for help n performng the experment n shootng pool. References:. B r o e k - M u c h a Z., Dfferentaton among varous types of ammunton by means of GSR examnaton, 6th ENFSI Frearms Workng Group Report 999, September 29 October, 999, Schevenngen, the Netherlands, p.. 2. B r o e k - M u c h a Z., SEM-EDX study of norganc gunshot resdues from Makarov 9 mm ammunton, Problems of Forensc Scences 2000, vol. XLI, pp B r o e k - M u c h a Z., J a n k o w c z A., Evaluaton of the possblty of dfferentaton among varous types of ammunton by means of SEM-EDX method, Forensc Scence Internatonal [n press]. 4. N e w o e h n e r L., Chemometrc Analyss of GSR data frst results, ENFSI Frearms Workng Group Meetng, Metropoltan Labolatory, The Forensc Scence Servce, London, N e w o e h n e r L., W e n z W., Applcaton of focused on beam systems n gunshot resdue nvestgatons, Journal of Forensc Scences 999, vol. 44, pp