Physical and chemical trace evidence from 3d-printed firearms, and use of a quadcopter for targeted sampling of gaseous mercury in the atmosphere

My forensic research resulted in the first peer-reviepaper to address the forensic challenges presented by 3D-printed polymer firearms. The work involved a systematic approach to the analysis of evidence stemming from 3D-printed firearms filling a critical void in current forensic knowledge. We used DART-MS to characterize the polymer evidence left behind by 3D-printed firearms as well as an evaluation of pre-existing firearm and toolmark techniques and fingerprint analysis. We demonstrated that 3D-printed firearms leave behind characteristic polymer residue on cartridge cases bullets and the receiving surface which can be identified using DART-MS. The culmination of the work includes a database / reference library that can give forensic practitioners the ability to identify and source unknown polymer evidence using chemometric analysis including principle component analysis (PCA) and ongoing work with supervised statistical classification methods. Several novel analytical methods were developed in the course of this dissertation work including forensic analysis of trace chemical evidence from 3D-printed firearms using direct analysis in real time-mass spectrometry (DART-MS) and targeted aerial sampling for quantitation of gaseous mercury. The mercury project utilized a quadcopter unmanned aerial vehicle (UAV) and gold-coated quartz sorbent tubes to target and capture gaseous mercury which was then quantified both in the laboratory and in the field using cold vapor atomic fluorescence spectrometry (CVAFS). This method was verified to effectively capture and quantify mercury in the atmosphere near point sources and was applied near a coal-fired power plants petroleum refinery and municipal landfill. Average concentrations (± standard deviation) immediately downwind of the landfill were higher at ground level and 30 m compared to 60 m and 120 m (5.3 ± 0.5 ng m-3 5.4 ± 0.7 ng m-3 4.2 ± 0.7 ng m-3 and 2.5 ± 0.3 ng m-3 respectively). Concentrations were also higher at an urban/industrial area (Memphis) (3.3 ± 0.9 ng m-3) compared with a rural/background area (1.5 ± 0.2 ng m-3). Overall we shothe method is useful to probe Hg concentrations aloft and quantify emissions from potential point sources in the field using an inexpensive quadcopter and sampling setup. The forensic research was funded by NIJ Graduate Research Fellowship (Award # 2017-IJ-CX-0001). The opinions findings and conclusions or recommendations expressed here are those of the authors and do not necessarily reflect those of the U.S. Department of Justice