Freshwater diatom persistence on clothing I: A quantitative assessment of trace evidence dynamics over time

Forensic botany: who?, how?, where?, when?

Plants are a good source of biological forensic evidence; this is due to their ubiquity, their ability to collect reference material, and their sensitivity to environmental changes. However, in many countries, botanical evidence is recognised as being scientifically. Botanical evidence is not mostly used for perpertration, instead it tends to serve as circumstantial evidence. Plant materials constitute the basis, among others, for linking a suspect or object to a crime scene or a victim, confirming or not confirming an alibi, determining the post-mortem interval, and determining the origin of food/object. Forensic botany entails field work, knowledge of plants, understanding ecosystem processes, and a basis understaning of geoscience. In this study, experiments with mammal cadavers were conducted to determine the occurence of an event. The simplest criterion characterising botanical evidence is its size. Therefore, macroremains include whole plants or their larger fragments (e.g. tree bark, leaves, seeds, prickles, and thorns), whereas microscopic evidence includes palynomorphs (spores and pollen grains), diatoms, and tissues. Botanical methods allow for an analysis to be repeated multiple times and the test material is easy to collect in the field. Forensic botany can be supplemented with molecular analyses, which, although specific and sensitive, still require validation.

Macroscopic assessment of environmental trace evidence dynamics in forensic settings

Environmental trace evidence offers useful circumstantial intelligence to link persons and scenes of forensic interest. An increasing empirical research base is dedicated towards understanding the transfer and persistence dynamics of environmental indicators including pollen, soils, and diatoms, within a diverse range of experimental frameworks. This paper presents two discrete studies exploring transfer and persistence of soils and sediments on footwear and diatomaceous earth adhered to clothing in forensically pertinent scenarios. Variables including sediment type, foot position, clothing type, and body positioning were also explored throughout. Both experiments incorporated a field-based methodology during the sampling effort. Photographs were collected of an initial transfer sample and of a retained assemblage following hours, days, and up to one-week of wear, facilitating macroscopic assessment of trace evidence dynamics. All images were processed using accessible, open-source software before spatial analysis of evidence distribution within and temporal assessment (% retention) upon each evidential surface. The results highlighted consistent loss of transferred sediment from footwear with significantly greater retention of loamy clay soil than dune sand which was absent beyond 24 h of wear. Loss was not influenced by wearer gait but was more rapid from those areas of the shoe sole in direct contact with the ground. Diatomaceous earth was retrieved from all three clothing types tested after one week - significant losses of material occurred before 48 h with a consistent assemblage identified beyond this. Denim was significantly more effective than acrylic and fleece for diatomaceous earth retention and significantly more material was lost from clothing worn on the lower body. These findings highlight the value of using visual environmental markers and a macroscopic analytical approach during the investigation of environmental trace dynamics. The methodology offers a novel, non-destructive assessment of soil and diatom transfer and persistence, complementing more extensive laboratory-based examinations to ensure the development of a well-rounded research base within the forensic sciences.

A fresh scientific look at transfer and persistence: From a materials science and tribology perspective

Knowledge of the mechanisms governing transfer, persistence, and recovery of trace evidence, together with background prevalence in the population of interest, and other task relevant information, is key for the forensic interpretation and reconstruction of what happened at the activity level. Up to now, this informational "toolkit" has largely been developed through empirical forensic studies on specific trace materials such as glass, textile fibers, and soil. Combined with the identified systemic siloing between disciplines, while valuable, such research tends to be very material-dependent, introducing specific parameters and interpretations that may have actually impeded the recognition of underlying foundational factors applicable to most material types. In Australia, there has been a renewed interest in developing a discipline-independent framework for the interpretation and/or reconstruction of trace evidence to interpret specific circumstances in casework. In this paper, we present a discipline agnostic "way of thinking" that has been anchored in foundational science underpinning the trace evidence discipline. Physical and mechanical material properties such as material geometry and surface topography, strength, stiffness, and hardness collectively influence contact interactions through underlying friction, wear, and lubrication cause and effect mechanisms. We discuss how these fundamental factors and parameters stemming from materials science and tribology may be adopted and adapted by forensic practitioners and researchers to contribute to a better understanding of transfer, persistence, and recovery mechanisms irrespective of evidence discipline and material type. Examples are provided to demonstrate the practical significance to real-life casework and academic research.