Trace DNA recovery rates from firearms and ammunition as revealed by casework data

Understanding casework DNA recovery rates per evidence type is crucial for advancing forensic methodologies and practices. This study assesses DNA recovery and profile data for 17 firearm parts (including cartridges, bullets and cases: CBCs) using New South Wales firearms casework data from 2015 to 2019. CBCs were further classified as shotgun or metallic cartridges and as unfired or fired. Quantitative data analysis showed that the least DNA was recovered from the hammer, safety and CBCs, while a single swab of multiple firearm parts resulted in the highest DNA recovery. Shotgun and unfired cartridges yielded more DNA than metallic and fired cartridge cases, respectively. Additionally, DNA collected from exhibits after fingerprinting yielded more DNA than exhibits sampled for DNA without any fingerprint examination. Profile data analysis showed that at least 64% of samples were unusable in casework. Cumulatively swabbed areas were most likely to produce usable profiles. Up to 22% and 38% of usable and unusable profiles, respectively, were mixed. Internal parts of the firearms had lower percentages of mixed profiles. The results from the data suggest the areas to prioritize for DNA recovery from firearms and highlights the need for further research to improve sample collection from firearms and ammunition.

明确不同证据类型下案件物证的DNA回收率，对于推动法医物证技术方法与实践发展具有重要意义。本研究依托2015至2019年新南威尔士州枪支案件物证数据集，针对17种枪支部件（包括弹筒、弹头与弹壳，即Cartridges, Bullets, Cases，简称CBCs）的DNA回收率与基因分型数据展开评估。研究进一步将CBCs划分为霰弹枪弹筒与金属弹筒，并分为未发射与已发射两类。定量数据分析结果显示，从击锤、保险装置与CBCs中提取的DNA量最少，而单次擦拭多个枪支部件可获得最高的DNA回收率。霰弹枪弹筒与未发射弹筒的DNA回收率分别高于金属弹筒与已发射弹壳。此外，经指纹检测后提取的物证DNA回收率，高于未经过任何指纹检测直接采样的物证。基因分型数据分析显示，案件物证中至少64%的样本无法获得有效分型结果。多区域累计擦拭的样本最易获得可用基因分型结果。可用分型与无法分型样本中，混合分型的比例分别可达22%与38%。枪支内部部件的混合分型比例更低。本研究结果明确了枪支物证DNA提取的优先检测区域，并强调需开展进一步研究以优化枪支与弹药的样本采集流程。