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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.

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Investigations at crime scenes after criminal acts involving gunshot injuries have occurred often encompass the analysis of traces of blood and so-called backspatter. Molecular genetic analysis of backspatter generated by contact shots and shots from very short distances has already been demonstrated to critically contribute to victim identification and the reconstruction of firearm-related crimes. Herein, we investigated the effect of several combinations of shooting distances and types of firearms on backspatter generation and co-extraction and simultaneous analysis of DNA and RNA isolated from traces of backspatter. Additionally, we assessed whether "triple contrast" doping of ballistic models interferes with forensic analysis of DNA, mtDNA and co-extracted mRNA and miRNA from backspatter collected from inside parts of firearms generated by experimental shootings. We show the effect of shooting distance and the type of firearm in experimental shootings on the yields of DNA and RNA co-extracted from backspatter and the success rates of forensic DNA profiling and RNA based organ identification. Furthermore, we demonstrate that "triple contrast" stained biological samples collected from inside surfaces of firearms are amenable to forensic DNA profiling and permit analysis of the entire mtDNA D-loop even for "low template" DNA amounts that preclude standard short tandem repeat DNA analysis.