Qualitative and semi‐quantitative primary and secondary transfer of metal traces by human touch detected using <scp>SEM</scp> – <scp>EDS</scp> technique: A pilot study

The present pilot study aimed to assess the transfer of metal residues on fingertips after contact with different items (primary transfer) as well as the transfer of metal residues by human fingertips from metal objects to different surfaces (secondary transfer). In the first part of the experiment, one volunteer touched 10 metal items with different characteristics and, after each touching, a single fingermark was collected using a stub. In the second part, a volunteer touched each of the objects and then another surface (glass, plastic, or the skin of a second volunteer). After each touching, a sample was collected using a stub from the touched surface. Then, the stubs were observed using a scanning electron microscope, and metal traces were quantified and analyzed using energy-dispersive spectroscopy. The analysis revealed a strong presence of traces in the first touch samples: in all of them, more than 50% of the examined fields presented traces composed of the same elements revealed on the objects. The highest secondary transfer was observed on plastic, followed by skin and glass. Overall, the quantity of transferred particles is higher for metal items with a rough surface compared with smooth ones. In conclusion, this work provides experimental data that can be useful in a forensic setting, in order to link objects, actions, and people, and that can help in the difficult task of reconstructing the dynamics of a crime.