Firing distance estimation based on the analysis of GSR distribution on the target surface using ICP-MS—An experimental study with a 7.65mm×17mm Browning pistol (.32 ACP)

Simple gunshot residue analyses for estimating firing distance: Investigation with four types of fabrics

This work presents two simple methods for estimating the firing distance from the gunshot residues (GSRs) on fabric targets. Four types of fabric targets, namely twill weave denim cotton-polyester (80/20), jersey knitting 100% cotton, plain weave cotton-polyester (80/20) and plain weave cotton-polyester (60/40), were employed. The firing tests were carried out using these white fabrics as targets at distances of 5-100 cm, respectively. In the first method, digital images of the black GSRs on fabric materials were recorded inside an illuminated box and the inverted gray intensity values were plotted against the firing distances. Since the plots of all fabrics are not significantly different, the estimation of firing distance employs the same exponential curve for all test fabrics. Although simple, the imaging method is not suitable for dark-colored materials. A chemical-based method was therefore developed as an alternative method. In the second method, a small disposable microfluidic paper-based analytical device (μPAD) was employed for detecting Pb(II) extracted from the GSRs. The μPAD method uses the measurement of the length of a narrow band of a pink color resulting from reaction between rhodizonate reagent and the Pb(II) extract. The plots indicated that the data of thick denim material are significantly different to other test fabrics which are much thinner. These three fabrics share the same estimation curve. However, it is recommended that the separate estimation curve for denim materials must be used. Both methods are suitable for short range firing distance, no further than 60 cm, since at greater distances the inverted gray intensity and the 'band-length' methods are unable to detect the GSRs.

Ear as an alternative sampling site for GSR analysis following shotgun discharge

Detection of GSR particles potentially indicates that a person fired a gun or somehow involved to a shooting event. GSR on the shooter's hand, face, and clothing may disappear within hours and with sweat secretion, washing or cleaning to remove evidences. Due to its anatomical properties, ears are relatively protected; therefore, we aimed to identify GSR particles on ears, to compare its anatomical parts of ears, and compare ears with common GSR sampling sites, based on firing frequency. A 12-gauge semi-automatic shotgun was used. In the 4-week study, one shot in the first week, two consecutive shots in second week, three shots in third week, and five shots in fourth week were fired by six participants. Samples were taken from MAE, CA, and AAECA of both ears and common GSR sampling sites. The characteristic 3-component structure (Pb/Sb/Ba) of the samples was analyzed by SEM/EDX. Right CA was the most suitable area for sampling, which might be attributed to posture of body during targeting. Right ear was the most suitable area to take samples from CA or MAE in 3-shot group. Besides, left AAECA in 1- and 2-shot groups and the left MAE in 5-shot group were the most suitable areas for GSR sampling. In conclusion, ear seems to be a valuable alternative for detection of GSR particles, due to its complex anatomical structure potentially preventing loss of GSR with daily cleaning. Findings suggested that crime scene investigation teams and criminal laboratory staff should consider ear as a valuable alternative for GSR detection.

Detection of Pb, Ba, and Sb in Cadaveric Maggots and Pupae by ICP-MS

The concentrations of lead (Pb), barium (Ba), and antimony (Sb), characteristic of GSR, were determined in soil sediments and immature (larvae) of cadaveric flies of the family Calliphoridae, by inductively coupled plasma mass spectrometry (ICP-MS). This research refers to a case study from two real crime scenes in which the corpses were in an advanced state of decomposition. In case 1, the victim had holes similar to gunshot wounds, and in case 2, there was no evidence of perforations in the corpse. Soil sediment collection was performed at three different points of the terrain, at a minimum distance of 10 m from the corpse, for cases 1 and 2. In relation to the collection of immatures, larvae were collected in regions of the mouth, nose, and orifices similar to the entry of firearms projectile into the body, for case 1, and collection of larvae and pupae, located on the body and underneath it, for case 2. It was possible to detect and quantify the three elements of interest (Pb, Ba, and Sb) by ICP-MS in both sediment and cadaveric larvae. Concentrations of 4.44, 8.74, and 0.08 μg/g were obtained for Pb, Ba, and Sb, respectively, in the soil for case 1. For the case 2, the concentrations in Pb, Ba, and Sb were from 16.34 to 26.02 μg/g; from 32.64 to 57.97 μg/g and from 0.042 to 0.30 μg/g, respectively. In the larvae, Pb, Ba, and Sb were quantified in cases 1 and 2 with a concentration of 6.28 and 1.78 μg/g for Pb, 1.49 and 2.94 μg/g for Ba, 0.50 μg/g and <LD for Sb, respectively. These new results present the detection of characteristic elements of GSR in cadaveric larvae in humans in a real crime scene, besides highlighting the importance of the study of immature flies, using the ICP-MS technique in forensic analysis.