Three-step forensic approach for the differentiation of human and pig fingernail-like fragments: macroscopic examination, raman spectroscopy and histogenetic analyses

In 2019, archaeo-forensic excavations were conducted at an agricultural structure to find a missing person. Sieving operations in a pigsty uncovered 19 finds macroscopically similar to fingernails. In forensic contexts, the lack of adequate literature complicates distinguishing taphonomically altered or fragmented fingernails from other organic or inorganic debris, as well as differentiating human fingernails from non-human ones. This poses significant limitations for investigations. This study aimed to establish a reproducible approach for forensic scenarios similar in complexity. Experimental tests were performed on known human and pig nails, both fresh and buried for months or years. Two specimens per type (human and pig, fresh and buried) for a total of eight samples were analyzed using macroscopic, microscopic, undecalcified histological, and chemical methods. Raman spectroscopy with Sequentially Shifted Excitation (SSE™) technology proved crucial in species diagnosis, reliably differentiating human from pig samples despite varied post-mortem intervals (PMI). The 19 artefacts recovered in the forensic case were thoroughly examined using macroscopic and microscopic analyses, followed by advanced spectroscopic techniques, including Raman and reflection micro-FTIR analyses. These non-destructive, cost-effective methods not only excluded the possibility that the suspected fragments were fingernails but also identified the nature of 18 out of 19 samples. Seven samples were therefore selected for further histological and genetic analyses. Most finds were identified as pig bones, but genetic results were hindered by soil contamination. The critical role of nondestructive integrated analytical methods, particularly Raman spectroscopy, in species diagnosis and targeting precise analyses in challenging cases is highlighted.