Forensic Science

Forensic Science International 61 (1993) 75-84 Internatienid

Determination of firing distance and firing angle by neutron activation analysis in a case involving

gunshot wounds

Gerald0 Capannesl ‘*, Claudio Ciavola, Antioco Franc0 Sedda

Analytical Chemistry Laboratory. ENEA-Casaccia, Via Angdarese 301, 00060 Rome, Italy

(Received 3 June 1992; revision received 22 February 1993; accepted 22 April 1993)

Abstract

This paper reports the determination of the firing distance and a method for the evaluation of the tiring angle in a fatal incident caused by two gunshots. Neutron Activation Analysis (NAA) was used to determine the Sb pattern around the bullet entrance holes on a garment of the victim, and around bullet holes produced by different shots on test targets from the gun and ammunition under investigation. The calibration curves obtained at various distances and firing angles enabled the determination of the tiring distances and angles of the crime shots with a standard deviation of * 2 cm and & So, respectively.

Key words: Determination; Firing distance; Firing angle; Gunshot residues pattern; Neutron activation analysis

1. Introduction

The determination of the firing distance is often an important problem in incidents involving gunshot wounds. The gunshot range is routinely estimated by visually comparing the casework powder residue pattern on the garments or on the skin of the victim with the ones obtained from a series of test firings at known distances, using the same gun and ammunition [l]. A more reliable and accurate method is based on the analytical determination of the concentration of material ejected from

* Corresponding author,

0379-0738/93/$06.00 0 1993 Elsevier Scientific Publishers Ireland Ltd. All rights reserved. SSDI 0379-0738(93)01329-P

76 G. Capannesi et al. /Forensic Sci. ht. 61 (1993) 75-84

the bore of the weapon around the entrance hole of the bullet, which includes burned and unburned powder grains, carbonaceous particles, bullet jacket debris, shavings and dirt.

A colour reaction (Walker test) for the identification of incompletely burned residues [2], or various analytical methods (Atomic Absorption, Neutron Activation Analysis, Polarographic Techniques) for the determination of nitrites, copper, lead or antimony around the hole have been used [3,4]. The chosen element concentra- tion is usually determined in two ‘rings’ around the hole. The internal ring (‘ring of dirt’) is claimed not to depend on the tiring distance [5], and is usually used for the identification of the entrance hole of the bullet, as it contains dirt, primer residues and lead deposited or wiped from the projectile; moreover, the concentration of ele- ments in the internal ring can be altered by blood soaking [6]. In the outer ring, the concentrations of characteristic elements (nitrites, lead, antimony, copper) ejected from the gun are determined and compared with the ones obtained in a series of test- firing vs. distances, under the same experimental conditions. Usually, the higher the elemental concentration, the shorter the tiring distance, in accordance with a calibra- tion curve, which is characteristic for each gun and ammunition brand.

Powder residue patterns will vary significantly, not only as a result of a different barrel length, caliber or other characteristics of different weapons [7], but also with changes in primer, powder type and lot, and propellant loading. All of these parame- ters are generally different in different brands, because not all manufacturers use the same composition or the same raw materials in ammunition of the same caliber and bullet weight, and, also, the same brand can be subjected to changes in composition at different dates of manufacture.

The precision and accuracy of the tiring distance determination in case work is, in our experience, strongly dependent on the experimental accuracy in obtaining the calibration curve and on an accurate consideration of all the variables involved - i.e. differences in powder composition, possible overlapping of two or more powder patterns in multiple shots, differences in tiring angles, folded or woven garments.

In the present paper we present an example of the determination of tiring distance, and a method for the evaluation of tiring angle in an actual case.

2. Case report

A young woman was killed in Rome with two gunshots. One of the bullets entered the victim 20 cm under the left axilla, the other perforated the center of the back. The investigating magistrate required our laboratory to ascertain the distance and position from which the bullets were fired.

3. Experimental

The victim wore a white cotton T-shirt; only two small blood stains were found at the entrance holes of the bullets. A series of test firings at different distances and angles, using the same gun (Bernardelli 7.65) and ammunition brand under investi- gation, were performed on white cotton fabric targets. A square with sides of about 12 cm was cut from the T-shirt in correspondence with the two bullet entrance holes,

G. Capannesi et al. /Forensic Sri. ht. 61 (1993) 75-84 77

Fig. 1. Scheme used for the sampling of the test targets and of the garment of the victim. A total of 13 disks, each 16 mm in diameter, were collected around each bullet entrance hole (disk No. 0).

A

Y( cm 4B

24

@

-24

-48

\ /'

/" \ 1.

SHOT=2nd-murder-shot

-48 -24 0 24 48 -48 -24 0 24 48

X(cm) X(cm)

Fig. 2. Contour plot of Sb concentration on the T-shirt of the victim around the bullet entrance holes. (a) First shot pattern. (b) Second shot pattern.

78 G. Capannesi et al. /Forensic Sri. ht. 61 (1993) 75-84

and from each of the test shot-targets. All the fabric squares were placed in plastic vials and irradiated for about 20 h in the rotating rack (Lazy Susan) of the 1 Mw TRIGA reactor of the Institute of Casaccia. Thermal neutron flux was 2.6 x IO** n/cm*/s and flux homogeneity better than 99.85%. A primary analytical standard of pure Sb (Johnson and Matthey) was simultaneously irradiated and used for gamma spectra calibration and conversion to concentration units. After irradiation the sam-

A SHOT=l@cm-90" B SHOT=lScm-90'

-24

-48 -24 0 24 48 -48 -24 0 24 48

XC-1 X( cmj

SHOT=ZOcm-90" D SHOT=Xkm-90"

Yfcm 48

24

-24

-48 -24 0 24 48 -48 -24 0 24 48

X(cm) X(cn-4

Fig. 3. Contour plot of Sb concentration on the fabric test targets. The firing angle of the gun with the X and the Y axis was kept at 90”. (a) Target-gun distance: IO cm. (b) Target-gun distance: 15 cm.

(c) Target-gun distance: 20 cm. (d) Target-gun distance: 30 cm.

G. Capannesi et al. /Forensic Sci. Int. (1993) 61 75-84 19

ples were left for 2 weeks to allow the activity of 24Na produced during the irradia- tion to decay.

Portions from each of the targets and from the T-shirt of the victim were cut, in form of little disks, around the bullet holes, by following the scheme of Fig. 1. Data collection on each of the fabric disks was performed by using an ORTEC HP-Ge detector with FWHM of 1.68 KeV and efficiency of 29% at 1332 KeV, coupled to

-24

-48

SHOl=l5cm-6B'

\ I I I

B

YI cm 48

24

-24

-48

SHOT-15cm-45"

/ Y

-48 -24 0 24 48 -48 -24 0 24 48

X(cm) X(cm)

C SHOT-15cm-30"

-48 -24 0 24 48

X(cm)

Fig. 4. Contour plot of Sb concentration on the fabric test targets. The target-gun distance was kept at 15 cm, and the angle of the gun with the X axis was kept at 90”. (a) Angle of the gun with the Y axis:

60”. (b) Angle of the gun with the Y axis: 45”. (c) Angle of the gun with the Y axis: 30”.

80 G. Capannesi et al. /Forensic Sri. ht. 61 (1993) 75-84

24

0

-24

-48 -24 0 24 4P

X( cm) Fig. 5. Example of elliptical symmetry of Sb pattern for a firing angle of 30” with the Y axis. The ratio R = A/B was measured on the test targets at various tiring angles, and the obtained data used for the cali-

bration curve of R vs. firing angle.

a LIVIUS (Silena) 8 K channels Pulse Height-Multichannel Analyzer, for the mea- surement of the net area of gamma peaks. All results, after blank subtraction, were expressed as (pg of Sb)/(cm* of fabric).

The nuclear reaction used was ‘23Sb(n,y)124Sb, with ‘24Sb having a half-life of about 60 days; the peaks used for data evaluation were 602 KeV and 1691 KeV.

4. Results

The Sb concentrations obtained were reported on a X-Y plane, and a contour plot was obtained from raw data, after a spline smoothing algorithm [8].

The distribution of Sb around the two bullet entrance holes on the T-shirt of the victim is reported in Figs. 2(a) and 2(b), and Figs. 3(a)-3(d) show the distribution of Sb on the cotton fabric targets at various firing distances, with the projectile enter- ing perpendicularly to the target plane. The cloud of gunshot residues appears more and more spread out vs. distance, but always retains a circular symmetry.

Figs. 4(a)-4(c) show the effect of a variation in the impact angle on the target. It is clearly visible that the gun-to-target tilt angle affects the Sb distribution on the target. The generated pattern shows an elliptical symmetry, whose major axis lies on the tilt plane (Fig. 5).

G. Capannesi et al. /Forensic Sci. ht. 61 (1993) 75-84 81

A

2 c 0

n 58

C

e n 1

Disk = 0

r 10 20 30 e a Distance

B

Disk = 1 C 0 n

I 12- =---____ Q -.-...__

0 ‘.-.,

n ll-

P I@- e r 9-

IO 20 R r DistanceCcm) e 3

82 G. Capannesi et al. /Forensic Sri. ht. 61 (1993) 75-84

Disk = 2

r 10 20 30 e a DistanccCcm)

Fig. 6. Calibration curves of distance vs. Sb concentration per unit area on samples under investigation. The calibration curves were fitted to the experimental data obtained from fabric test targets (empty circles); numbered circles refers to murder shots. (a) Disk No. 0 data. (b) Disks No. I data. (c) Disks

No. 2 data.

Fig. 6(a) shows the Sb concentration in disk No. 0 (Fig. l), i.e. in the region immediately around the bullet entrance hole, for the test firing samples and for the two casework shots.

Figs. 6(b) and 6(c) show, respectively, the mean value of Sb concentration in the four disks No. 1 and in the four disks No. 2 (Fig. 1) for test and casework samples. The values of Sb concentration for disks No. 4 are very low, and were not used in data treatment due to their much lower precision and reliability. It is clearly visible from the three series of disks (No. 0, No. 1 and No. 2) how quite consistent distances for the two workcase shots can be evaluated. The distance value for shot 1 is 16.5 cm f 0.3 cm, for shot 2 is 26.7 f 0.4. The reported standard deviation is evaluated from the three series of data; by introducing the uncertainty due to the curve fitting error, a total uncertainty of f 2 cm is obtained, which is quite consis- tent with the common accepted value of 0.5-l inch for standard deviation in ac- curate firing distance determinations [4].

G. Capannesi et al. /Forensic Sci. ht. 61 (1993) 75-84 83

1 I 03 1.08 1.13 1.18 lo23 1 I28 1.33 1 I38 1.43

maJcr axls/m:nor axis

Fig. 7. Calibration curve of R = (major axis)/(minor axis) (see Fig. 5) vs. firing angle. The calibration curve was fitted to the experimental data from fabric test targets (empty circles); numbered circles refers

to murder shots.

The mean value of the four disks of the scheme of Fig. 1 was used for distance evaluation in Figs. 6(b) and 6(c) (disks No. 1 and No. 2, respectively), which is equiv- alent to performing the analytical determination on a ring of fabric.

By mapping the concentration of each disk on a X-Y plane, a check of anomalous tiring conditions (overlapping of multiple shots, folded clothing, shadowing of the gunshot by an obstacle or an arm, and so on) can also be performed.

Apart from this, the mapping according to Fig. 1 enabled us to perform an evalu- ation of the tiring angle. The ratio R = (major axis)/(minor axis) (see Fig. 5) was measured for the patterns on test targets, and a polynomial calibration curve was fitted to the experimental data. The same ratio, R, was measured on the T-shirt under investigation, and the values obtained from the calibration curve for the tiring angles for shots 1 and 2 were, respectively, 45” and 83”, with an evaluated uncertain- ty of f 5”. These two points are shown in Fig. 7.

5. Discussion

The analytical determinations by NAA of gunshot residues on a garment enabled the estimation of firing distances and angles in a case involving gunshot wounds. The examination of contour plots of the pattern of Sb distribution on the garment

84 G. Capannesi et al. / Forensic Sri. Ini. 61 (1993) 75-84

around the bullets’ entrance holes not only permits higher precision in distance determination to be reached, but also gives the possibility of an evaluation of the uncertainty, and a check of possible anomalous tiring conditions.

Moreover, a method was proposed for the evaluation of tiring angles by the use of a calibration curve on test shots at various angles.

References

R.R. Saferstein, Forensic Science Handbook, Prentice Hall, Englewood Cliffs, NJ, 1982, p. 588. J.T. Walker, Chemistry and legal medicine. N. Engl. J. Med., 216, (1937) 1026-1027. S.S. Krishnan, Firing distance determination by neutron activation analysis. J. Forensic Sci., 12 (1967) 471. S.S. Krishnan. Firing distance determination by atomic absorption spectrophotometry. J. Forensic Sci., 19(2) (1974) 351-356. P. Bergman and Z. Zeichner, Firing distance determinations employing the blackening around bullet holes. Internal Report 248, Israeli Police, C.I.D., 1984. H. Even, P. Bergman, E. Springer and A. Klein, The effects of water-soaking on firing distance estimations. J. Forensic Sci., 33(2) (1988) 319-327. F.C. Barnes and R.A. Helson, Empirical study of gunpowder residue patterns. J. Forensic Sci., 19(3) (1974) 448-462. J. Meinguet, Multivariate interpolation at arbitrary points made simple. J. Appl. Math. Phys., 30 (1979) 292-304.