A distant relationship?-investigation of correlations between DNA isolated from backspatter traces recovered from firearms, wound profile characteristics, and shooting distance

Abstract

In molecular ballistics, where traces originating from the use of firearms against biological targets are investigated, "backspatter" traces are of particular importance. This biological material comprising blood and tissue from the victim is propelled back from the bullet entry site towards the direction of the shooter and can consolidate and persist on the inner and outer surfaces of the firearm, from where it can be collected and analyzed. Thus, a connection between the weapon and the victim can be established solely by molecular biological trace analysis. For the criminalistic investigation of gun-related crimes, the determination of the distance between the weapon and the victim can be of critical importance in reconstructing the circumstances of a crime. In this study, we investigated possible correlations between the shooting distance and the amount of backspatter in/on the used firearm. To this purpose, we employed a previously established skull model and performed shootings in triplicates from various distances up to 50 cm with two types of handguns (pistol and revolver). Backspatter was collected from various sampling locations, and DNA contents were quantified. A post-shooting wound channel evaluation was conducted by optical and radiological evaluation. The obtained DNA yields varied considerably between replicates from the same and from different distances. In contrast, apart from contact shots, no meaningful differences were observable in wound channel evaluations. In summary, no meaningful correlation between backspatter distribution and DNA yields, the shooting distance and the condition of the wound channel could be established.

Keywords: Backspatter; Ballistic model; Firing distance; Molecular ballistics; Shooting distance; Wound channel.

Fig. 1

Distribution of DNA yields after pistol shots. Pie chart depicts the sums of the triplicates’ quantified DNA, extracted from all backspatter traces for the indicated shooting distances. Bar charts show the distribution of values at each sampling location as the sum of the triplicates. A Outside surface of the frame and slide. B Inside surface of the barrel. C Outer surface of the barrel and area around the recoil spring (open slide). X Other surfaces (backside of slide)

Fig. 2

Distribution of DNA yields after revolver shots. Pie chart depicts the sums of the triplicates’ quantified DNA, extracted from all backspatter traces for the indicated shooting distances. Bar charts show the distribution of values at each sampling location as the sum of the triplicates. A Outside surface of the frame. B Inside surface of the barrel. X Other surfaces (cylinder, trigger guard, recoil shield)

Fig. 3

Combined polygon perimeter results by optical evaluation. Gelatin brain simulants were removed from the skull models 24 h after shooting and cut into 1-cm slices perpendicularly to the trajectory and scanned for optical evaluation using ImageJ v.1.52. Projected values are means of the three shots, with standard deviation. a Results after shots with Glock 19, 9-mm Luger. b Results after shots with Smith & Wesson CGT 36, .38 Special