A modified trace metal detection test for secondary imprints on porous substrates: A preliminary study

The transfer and persistence of metals in latent fingermarks

Transfer and persistence of metals in latent fingermarks derived from objects of forensic interest explored using synchrotron sourced X-ray fluorescence microscopy.

A subsequent procedure for further deciphering weapons after application of the Trace Metal Detection Test (TMDT): Proof of concept

The trace metal detection test (TMDT) is an effective and convenient technique to potentially link perpetrators and metallic weapons by comparing morphological information of developed imprints and suspected weapons. However, metallic items without characteristic patterns and incomplete contact with weapons often lead to inadequate morphological features in developed imprints on hands, resulting in difficulty in identifying suspected weapons and a failure to demonstrate potential relationships between perpetrators and weapons. This paper presents a subsequent procedure, after application of the TMDT, for inferring possible weapon-source of a specific imprint. As a proof of concept, all the experiments involved metallic items as an example and were carried out under controlled laboratory conditions. An analytical method was established by selecting elements of interest in developed imprints from seven metallic items (three groups), undertaking quantitative ICP-MS determination of the elements, and comparing the elements in these imprints (inter- and intra-group comparisons) and with those in their source items. Using the established method, possible groups and types of source metallic items could be inferred based on elemental characteristics in imprints, under the premise that no other metal sources exist before or after contacting specified metallic items. This method could be useful for providing investigative clues and evidence of association for developed imprints that lack unique morphological features and for verifying the results of color reactions in the TMDT. For this reason, it can serve as a standard supplementary procedure after the application of the TMDT, which could further strengthen the correlations between perpetrators and weapons even common metallic objects.

Revealing the Elemental Distribution within Latent Fingermarks Using Synchrotron Sourced X-ray Fluorescence Microscopy

Fingermarks are an important form of crime-scene trace evidence; however, their usefulness may be hampered by a variation in response or a lack of robustness in detection methods. Understanding the chemical composition and distribution within fingermarks may help explain variation in latent fingermark detection with existing methods and identify new strategies to increase detection capabilities. The majority of research in the literature describes investigation of organic components of fingermark residue, leaving the elemental distribution less well understood. The relative scarcity of information regarding the elemental distribution within fingermarks is in part due to previous unavailability of direct, micron resolution elemental mapping techniques. This capability is now provided at third generation synchrotron light sources, where X-ray fluorescence microscopy (XFM) provides micron or submicron spatial resolution and direct detection with sub-μM detection limits. XFM has been applied in this study to reveal the distribution of inorganic components within fingermark residue, including endogenous trace metals (Fe, Cu, Zn), diffusible ions (Cl^-, K⁺, Ca²⁺), and exogeneous metals (Ni, Ti, Bi). This study incorporated a multimodal approach using XFM and infrared microspectroscopy analyses to demonstrate colocalization of endogenous metals within the hydrophilic organic components of fingermark residue. Additional experiments were then undertaken to investigate how sources of exogenous metals (e.g., coins and cosmetics) may be transferred to, and distributed within, latent fingermarks. Lastly, this study reports a preliminary assessment of how environmental factors such as exposure to aqueous environments may affect elemental distribution within fingermarks. Taken together, the results of this study advance our current understanding of fingermark composition and its spatial distribution of chemical components and may help explain detection variation observed during detection of fingermarks using standard forensic protocols.