Shining a Light on Forensic Anthropology: The Use of Alternative Light Sources to Detect Skeletal Remains Underwater

Abstract

Aquatic searches for human remains are time consuming and expensive, focused on locating intact cadavers rather than bone. Once a body becomes skeletonised it is more vulnerable to the destructive mechanics of currents and tides, leading to fragmentation, dispersal, and modification of the bone surface. This makes locating and identifying bone even more challenging. Alternative light sources (ALS) are a crime scene staple, routinely used to locate body fluids such as semen and saliva, by stimulating the natural autofluorescence of proteins. This process is non-contact, and non-destructive, used to reveal latent evidence and facilitate documentation and recovery. Bone also produces fluorescence when exposed to ALS, which is thought to be primarily due to the highly collagenous organic content.

This research united current strands of osseous ALS research by implementing a unique methodology combining thermogravimetric analysis (TGA) to quantify bone collagen, and a bespoke C++ computer program: The Osteo-Fluorescence Calculator (OFC) to quantify bone fluorescence, which enabled deeper interpretation of the collagen-fluorescence relationship, the taphonomic impact on bone autofluorescence, and its use in terrestrial and underwater crime scenes, not previously reported in literature.

Key results indicated that collagen is most likely the primary contributor to bone autofluorescence, and that the larger the collagen volume the greater the observed fluorescence intensity when photographed with blue light (450 nm) and orange filter in a terrestrial (p= .000) and underwater contexts (p= .000). However, differentiation and control studies suggest that bone colour, texture, and morphology may also influence fluorescence emissions, but differentiation between bone and other non-bone items is possible due to variable fluorescence intensities, including in an underwater context. Hot water was identified as a suitable preparation technique for bone undergoing ALS analysis, as it produced homogenous fluorescence, similar to pre-macerated values (p=.012), with limited collagen degradation (p= .023), whereas biological washing powder was destructive to bone collagen content (p= .000) and produced exaggerated and inconsistent fluorescence (p= .180).

Taphonomic studies confirmed that bone autofluorescence can be produced in terrestrial (p= .000) and submerged tap water environments (p= .000) when using blue light (450 nm) and an orange filter. Although underwater fluorescence levels were reduced compared to terrestrial findings, submersion in tap and seawater for 6-months led to a dramatic increase in bone fluorescence intensity (p= .000) and a minor reduction in collagen content (p= .000), which would aid dark, underwater searches. Comparatively, saltwater was no more destructive to porcine bone collagen than tap water, after submersion for 6-months (p= .000), indicating that ALS can be used to search for bone for at least 6-months after skeletonization.

Overall, this research demonstrated that effective ALS examination has the potential to help simplify search methodologies, reduce costs, speed up recovery, and triage findings, with implications for missing persons cases, crime scene investigation and archaeological contexts.