X-ray diffraction analysis of bone crystallinity and its association with postmortem interval in human skeletal remains.

Estimation of the postmortem interval in human skeletal remains persists as a major challenge in forensic anthropology. This study aimed to evaluate whether bone crystallinity parameters obtained by X-ray diffraction (XRD), namely crystallinity index (CI) and crystallite size, are associated with PMI. A sample of 38 human clavicles with known PMIs ranging from 4 to approximately 500 years was analyzed, together with an additional subsample of 12 burned clavicles (PMI = 4 years). The results showed no consistent relationship between crystallite size and PMI, with high variability across samples. In contrast, CI exhibited a moderate positive correlation with PMI (ρ = 0.587, p < 0.001; 95% CI: 0.194-0.810), with values generally increasing in older remains. However, substantial overlap was observed within the forensic timescale, limiting its applicability for precise PMI estimation. Additionally, variability among samples with identical PMI highlighted the influence of taphonomic factors, and thermal alteration was shown to affect crystallinity, potentially mimicking older remains. These findings suggest that, although XRD-derived crystallinity parameters provide useful insights into postmortem changes in bone mineral structure, their application for PMI estimation remains limited.