Persistence of biological traces in gun barrels—an approach to an experimental model

Abstract

Traces of backspatter in gun barrels after homicidal or suicidal contact shots may be a valuable source of forensic evidence. Yet, a systematic investigation of the persistence and durability of DNA from biological traces in gun barrels is lacking. Our aim was to generate a realistic model to emulate blood and tissue spatters in gun barrels generated by contact gunshots at biological targets and to analyse the persistence and typability of DNA recovered from such stains. Herein, we devise and evaluate three different models for the emulation of backspatter from contact shots: a gelatine-based model with embedded blood bags, a model based on a spongious matrix soaked with blood and covered with a thin plastic membrane and a head model consisting of an acrylic half sphere filled with ballistic gelatine and with blood bags attached to the sphere under a 3-mm silicone layer. The sampling procedure for all three models: a first shot was fired with several types of guns at each model construction and subsequently a second shot was fired at a backstop. Blood samples were collected after each shot by probing the inner surface of the front and rear end of the respective gun barrel with a sterile swab. DNA was then extracted and quantified and up to 20 different short tandem repeat (STR) systems were amplified to generate DNA profiles. Although DNA quantity and STR typing results were heterogenous between the models, all models succeeded in delivering full STR profiles even after more than one shot. We conclude that biological traces in gun barrels are robust and accessible to forensic analysis and that systematic examination of the inside of gun barrels may be advisable for forensic casework.

Persistence of Biological Traces at Inside Parts of a Firearm from a Case of Multiple Familial Homicide

“…The present investigation of a case of multiple homicide that integrates forensic ballistic and genetic methods corroborates our previous hypotheses as to backspatter from contact shots retrieved from within a firearm being a relevant source of profilable DNA , whereas forensic literature addressing the analysis of trace DNA so far ignored the inside surfaces of firearms as potential sources of profilable DNA .…”

“…Initially, in our former work, we were focused on the barrel inside only and showed that full DNA profiles could successfully be established from biological material recovered from within a firearm's barrel even after a second shot had been fired through . In the present case of multiple familial homicide, however, of all locations, the barrel was the one from where no profilable DNA could be recovered.…”

“…In previous studies, we presented the first systematic evaluation of integrity and profilability of victim DNA extracted from trace amounts of blood and/or tissue from backspatter generated by contact shots on the inside of firearms and applied these insights into several casework samples where we obtained satisfactory STR‐typing results in most cases even after a second shot had been fired through the barrel .…”

Characteristics of Backspatter on the Firearm and Shooting Hand—An Experimental Analysis of Close‐range Gunshots

“…Courts et al. examined biological traces in gun barrels after contact shots with different firearms. Similar to our setup, one of their models consisted of spongy material soaked with sample blood and clad in thin plastic.…”

On the effect of shooting distance, ballistic model construction, doping and weapon type on the simultaneous analysis of DNA and RNA from backspatter recovered from inside surfaces of firearms

“…Traces of backspatter may consolidate on and be recovered from the shooter and the shooter"s surroundings but also from inside surfaces of the firearm. However, such criminal acts involving shooting firearms at biological targets cannot be planned or controlled, therefore experimental shootings have to rely on standardized ballistic models [1,2] and recently, a new modelling method was presented that allows for the economic molecular analysis of DNA from backspatter with simultaneous investigation of wound ballistic phenomena [3]. Herein, we aim to extend this method"s versatility to include the analysis of mtDNA and RNA (project B).…”