Hart Andrew J, Barnes Geoffrey C, Fuller Fiona, Cornwell Amy M, Gyula Judit, Marsh Nick P
Forensic Services, Metropolitan Police Service, 109 Lambeth Road, London SE1 7LP, UK.
Strategy and Governance, New Scotland Yard, Metropolitan Police Service, Victoria Embankment, London SW1A 2JL, UK.
Forensic Sci Int. 2022 Jan;330:111124. doi: 10.1016/j.forsciint.2021.111124. Epub 2021 Nov 26.
The use of infrared (IR) light to locate bloodstains on dark fabric is a search technique that is employed in forensic examinations in a number of organisations worldwide. IR is used to complement existing, established visual white light search techniques. There exist a variety of commercially available products that can be purchased for this purpose as well as the option of using IR-converted standard DSLR (Digital Single Lens Reflex) cameras. In this study, a number of IR systems with contrasting resolutions were explored and their performance was assessed on a variety of bloodstain types and fabrics in comparison with white light. The systems ranged from low-budget, low resolution options, such as portable webcams, to vision-industry standard, high resolution, purpose-built cameras for more detailed blood searching of suitable items in the laboratory. Blood spatter, transfer bloodstains, dilute bloodstains, blood mixed with other body fluids and environmental contaminants were among the samples tested on eight different dark fabric types under IR conditions to assess the impact of the resolution differences. All IR systems were able to locate bloodstains, with significantly more bloodstains being found with IR compared to white light. The higher resolution systems were able to locate significantly more bloodstains than the systems with the lower resolution. The webcams were able to locate many of the larger areas of bloodstaining but performed less well in terms of locating smaller bloodstains and dilute blood. False positives such as mud, make-up and brown sauce were detected under IR but were readily discriminated under white light and with presumptive chemical tests. The balance between the ability to locate bloodstains based on system resolution and practicality and possible efficiency gains is discussed.
利用红外（IR）光在深色织物上定位血迹是一种搜索技术，全球许多组织都在法医检查中使用。红外用于补充现有的、既定的可见光搜索技术。有多种可用于此目的的市售产品，也可以选择使用红外转换的标准数码单反（Digital Single Lens Reflex）相机。在本研究中，探索了一些分辨率不同的红外系统，并与白光相比，在各种血迹类型和织物上评估了它们的性能。这些系统范围从低预算、低分辨率的选项，如便携式网络摄像头，到视觉行业标准的、高分辨率的、专门用于在实验室对合适物品进行更详细血迹搜索的相机。在红外条件下，对八种不同深色织物类型的样本进行了测试，其中包括血迹喷溅、转移血迹、稀释血迹、与其他体液混合的血液以及环境污染物，以评估分辨率差异的影响。所有红外系统都能够定位血迹，与白光相比，红外发现的血迹明显更多。分辨率较高的系统比分辨率较低的系统能够定位更多的血迹。网络摄像头能够定位许多较大的血迹区域，但在定位较小的血迹和稀释血迹方面表现较差。在红外条件下检测到了诸如泥土、化妆品和棕色酱汁等误报，但在白光下以及通过推定化学测试很容易区分。讨论了基于系统分辨率定位血迹的能力与实用性以及可能的效率提升之间的平衡。
