Comparison of three DNA extraction methods for three different types of fired and unfired ammunition

When handling ammunition for gun loading, epithelial cells from the hands can become adhered to the metal surface, and this trace is a potential source of DNA. This work aimed to compare the efficiency of three DNA extraction methods from fired cartridge cases from three different types of firearms: a 12-gauge shotgun, a point 40 S&W pistol, and a 7.62 mm rifle. Nine volunteers were involved in this study handling 42 pieces of ammunition overall. The unfired ammunition was handled by a known good donor, and we used this data for comparison. DNA profiling was carried out with EZ1 DNA Investigator Kit for EZ1 Advanced XL automated DNA extraction, QIAmp DNA Investigator kit for a non-automated silica-based membrane column method, and direct lysis protocol for a non-automated in-house one. Samples were collected with 0.5 × 0.5 cm pieces of FTA filter paper moistened with distilled water. Quantiplex Pro RGQ kit and Fusion Powerplex 6C were used for genotyping samples. QIAmp DNA Investigator method resulted in the best number of alleles recovered for both conditions tested, both unfired and fired ammunitions: 77 % vs. 19.3 %, followed by the automated extraction (28.6 % vs. 4.3 %) and lysis protocol (0 % vs. 3.9 %). Degradation data from fired cartridge cases were 27 % for column method, 50 % for lysis protocol, and 87 % for EZ1 kit. Kruskal-Wallis test for mean DNA concentration from these samples returned p < 0.05, and Dunn’s multiple comparison test indicated a significant difference between calibers 0.40 S&W and 12-gauge shotgun from lyses protocol method. We did not detect any other significant differences on the test. The 12-gauge shotgun cartridge cases resulted in a high number of alleles overall (56.8 %). The numerous steps for DNA extraction and purification in the column method may explain its better performance. Although the results obtained indicate that all methods be used for DNA extraction from this type of evidence, the silica-based membrane column method appears to be more efficient.     

Preliminary investigations using Recover Latent Fingerprint Technology on unfired ammunition and fired cartridge cases

Previous studies have identified the potential benefit of the disulfur dinitride (S₂N₂) process to operationally relevant substrates. However, the majority of this work was conducted on prototype equipment that had substantial differences to the commercialised system (Recover Latent Fingerprint Technology (LFT)) in terms of design and chemical delivery. This paper evaluates the performance of Recover LFT on a problematic exhibit encountered within a fingerprint enhancement laboratory: unfired and fired ammunition. Three pseudo-operational experiments involving non-groomed, naturally handled fingermarks were conducted on the most commonly encountered types of ammunition used in crime in the United Kingdom (UK). In addition, Recover LFT was compared against Superglue Fuming followed by Basic Yellow 40 (BY40) Fluorescent Dye Staining (a commonly used alternative) to ascertain if the process provides added benefit to fingermark recovery rates. The results show that fingermark visualisation on small calibre cartridge cases remains difficult with few marks achieving enough ridge detail for comparison. However, this paper also shows that the novel Recover LFT process, which is still in its infancy and requiring optimisation, is no worse than currently implemented visualisation processes and is therefore worth further investigation.     

子弹弹头及弹壳成分比较研究

目的对子弹物证进行成分分析可为涉枪案件的侦查提供科学依据。本实验旨在通过研究子弹弹头及弹壳的元素组成快速区分不同子弹,为推断子弹来源提供关键信息。方法收集不同厂家在1958-2019年不同批次生产的多种型号的子弹样品53份,应用扫描电镜能谱法(SEM/EDX)对样品的弹头内芯、弹头披甲和弹壳金属成分进行研究。结果结果显示多数子弹弹头内芯由纯铅构成,部分批次较晚的弹头为铅锑合金,另有两枚批次较早子弹为铁弹头;除六枚5.6mm运动步枪弹的弹头披甲以及四枚791厂样品的弹壳无明显特征外,其余子弹的弹头披甲和弹壳均为三类铜锌合金中的一种:含铜量83.7%~84.7%、87.6%~90.6%以及67.0%~69.8%的铜锌合金。同型号同厂家子弹所使用弹头披甲及弹壳材料的特征相似,同型号不同厂家、同厂家不同型号的子弹弹头披甲和弹壳材料则具有一定差异。近六十年来121厂样品子弹弹头披甲均为含铜量87.6%~90.6%的铜锌合金,弹壳材料为含铜量67.0%~69.8%的铜锌合金,其为该厂固定使用的铜锌合金原材料的可能性较高。791厂样品中有四种型号的子弹弹壳均为含锰量0.7%~0.9%的铁锰合金,这种合金在其他厂家并未出现,其为791厂弹壳特征原材料的可能性较高。结论掌握子弹弹头及弹壳的元素组成特征可以对不同子弹进行有效识别。     

Development of STR profiles from firearms and fired cartridge cases

Fired cartridge cases are a common type of evidence found at crime scenes. However, due to the high chamber temperatures and touch nature of this evidence, DNA testing is not commonly sought because it is believed DNA is only present in low levels, whether it is due to initial low levels of DNA and/or DNA degradation from the heat or inhibition of the PCR reaction. Moreover, very few laboratories report STR typing success with fired cases. This study focused on obtaining STR profiles from fired cartridge cases using the AmpFℓSTR^® MiniFiler™ kit, which is designed to amplify DNA from low level, inhibited, and degraded samples. Comparisons to other STR amplification kits were also conducted. In attempt to simulate casework, random individuals loaded cartridges into a firearm. DNA was recovered from the fired cartridge cases using the double swab technique and extracted using an automated large volume DNA IQ™ method. Initially, testing focused on known shedders handling cartridges for 30 s prior to firing. A significantly greater number of alleles was obtained following amplification with the MiniFiler™ kit versus the PowerPlex^® 16 BIO kit. No alleles were observed using the Identifiler^® kit. In an attempt to better simulate casework, a random selection of laboratory personnel handled shotshells for as long as needed to load and fire the weapon. In this mock sample study, the MiniFiler™ kit successfully amplified an average of 22% of expected alleles from DNA recovered from shotshell cases versus the PowerPlex^® 16 BIO kit where an average of 7% of alleles were observed. However, the total number of alleles obtained from the two kits was not significantly different. The quality of the DNA obtained from fired cases was studied with evidence of inhibition in at least 11% of shotshell case samples. After swabbing the head and the hull of three shotshell cases separately, a significantly greater number of alleles was obtained from the hull as opposed to the head of the fired shotshell case. In addition, after firing, various internal firearm surfaces were swabbed, including the chamber of barrel, ejection port, and breechface, in an attempt to obtain amplifiable DNA. DNA was obtained from the chamber of the barrel and was amplifiable using the MiniFiler™ kit, although mixtures were obtained with extensive drop-in and drop-out making this analysis unlikely to aid an investigation.     

Towards the protection of ammunition headstamps during fingermark enhancement processing; a preliminary study

Forensic recovery from fired ammunition casings remains one of the most challenging tasks during high-profile investigations. Often, the decision must be made between screening for DNA or fingerprints, and, in doing so, the impact these processes will have on the examination of ballistic markings imparted on the ammunition from the firearm itself. Traditionally, fingermark enhancement processes have yielded low success rates in their efforts to identify suspects by enhancing friction ridge detail left on the cartridge casings. Moreover, the enhancement methods utilised may often induce detrimental physical changes to the casing(s), rendering them unsuitable for subsequent ballistics (marking) examination. Recently, new technology has been shown to increase the success rate of fingermark recovery from fired ammunition, and the growing adoption of such innovation means that new challenges are encountered to maximise evidence recovery and streamline forensic workflows. One such example arises from the potential obscuration of the ammunition headstamp area during such treatments. Accordingly, this study outlines the preliminary investigations and developments of a polymer mask substrate that serves to protect the headstamp of fired ammunition casings during relevant fingermark enhancement processes. The technique also has the capacity to be used as a surface protection device to eliminate unwanted chemical deposition across other areas of interest and evidence types.