Harte, A., Cassella, J. P., & McCullagh, N. A. (2020). Recovery of trace evidence in forensic archaeology and the use of alternate light sources (ALS). Forensic Science International, 316, Article 110475. doi.org

This 2020 study by Harte et al. evaluated the novel field application of an alternate light source (ALS) during archaeological excavations to improve the recovery of trace evidence from clandestine graves. In a controlled experiment, three archaeologists excavated six test pits that had been seeded with micro-evidence (20 bone fragments \(\le \)10 mm, 16 hair fibers, two fabric pieces, and two lead pieces) and backfilled for over 15 weeks, with each participant digging one pit in daylight and one inside a darkened tent using a blue 455 nm ALS. The results showed that while overall trace evidence recovery was slightly higher in daylight (46% average) than under ALS conditions (40% average), smaller bone fragments (\(\le \)5 mm) were more than twice as likely to be detected and recovered when using the ALS. Conversely, non-fluorescent materials like lead were heavily overlooked under ALS (17% recovery versus 83% in daylight), and the darkened tent environment resulted in a 47% higher dimensional excavation error rate. Noting a strong positive correlation between an excavator's field experience and recovery success, the authors concluded that ALS should not be used as a standalone excavation method, but serves as an excellent supplementary tool for on-site soil sieving and post-excavation grave cut inspections.

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