Discussion

The present study explored the postmortem application of Bioelectrical Impedance Analysis in a forensic setting and provides novel data on the behavior of bioelectrical parameters in relation to the postmortem interval. The results confirm that BIA is technically feasible in human cadavers under routine medico-legal conditions and that specific electrical parameters exhibit time-dependent changes after death [12–14]. Among the evaluated variables, phase angle showed the strongest observable association with PMI, although the correlation remained moderate and characterized by substantial overlap between different PMIs.

The observed moderate positive correlation between phase angle and PMI represents one of the key findings of this study. This result is particularly relevant because it highlights a divergence between postmortem and in vivo bioelectrical behavior. In clinical settings, phase angle is widely interpreted as a marker of cellular integrity and membrane functionality, with lower values associated with membrane breakdown, fluid imbalance, and adverse outcomes [15–17]. In the postmortem context, however, the biological meaning of phase angle must be reconsidered. After death, the cessation of active cellular processes leads to the progressive loss of transmembrane ion gradients, increased membrane permeability, and redistribution of intra- and extracellular fluids [18]. These changes do not result in an immediate collapse of tissue structure but rather in a gradual transformation of the body into a more electrically homogeneous and passive system. One possible explanation for the observed increase in phase angle is the progressive transition of the body from an actively regulated biological system toward a progressively passive and electrically homogeneous structure. However, this interpretation remains hypothetical and requires dedicated experimental validation. Future studies based on controlled in vitro tissue models and computational simulations of postmortem electrical propagation may help clarify the physical mechanisms underlying these observations.

At present, the biological and physicochemical mechanisms underlying postmortem bioelectrical changes remain insufficiently understood. Consequently, the observed associations should not be interpreted as evidence of a validated thanatochronological mechanism but rather as exploratory observations requiring further mechanistic investigation.

Reactance showed only a weak association with PMI, while resistance and impedance demonstrated no meaningful correlation with postmortem time. These findings suggest that parameters primarily reflecting tissue conductivity and total body water are strongly influenced by inter-individual variability and postmortem fluid shifts, which may obscure time-dependent trends. In contrast, phase angle, which integrates both conductive and capacitive properties, showed a comparatively stronger association with PMI within the limitations of the present dataset. These findings suggest that different bioelectrical parameters may respond differently to postmortem changes and should therefore be interpreted cautiously in forensic settings.

BMI was included only as an exploratory variable potentially influencing bioelectrical measurements. Given the limited sample size and the absence of multivariate modeling, no definitive conclusions regarding the confounding role of BMI can be drawn.

Exploratory regression modeling provided additional insight into the temporal behavior of phase angle. The log-linear relationship observed between phase angle and PMI suggests that postmortem electrical changes may evolve more rapidly during the early postmortem period and progressively stabilize at longer intervals. This pattern is biologically plausible, as early postmortem changes are characterized by rapid ionic redistribution and membrane permeability alterations, followed by slower structural degradation. However, despite improved model fit compared with a simple linear approach, residual variability remained substantial, indicating that phase angle alone cannot provide precise individual-level PMI estimates. Phase angle may provide limited supplementary temporal information; however, the current findings do not support its use as a reliable method for PMI estimation.

An important methodological contribution of this study concerns the effect of forensic autopsy procedures on bioelectrical measurements. In all cases with paired pre- and post-autopsy recordings, phase angle values increased after autopsy, independent of PMI or BMI. This systematic effect suggests that invasive postmortem procedures significantly alter tissue electrical behavior, likely through anatomical disruption, loss of compartmental integrity, and redistribution of fluids. This finding may be relevant for the interpretation of postmortem bioelectrical measurements, as it indicates that post-autopsy BIA measurements are not directly comparable to pre-autopsy values and may introduce substantial bias if measurement timing is not standardized. Consequently, if BIA is to be integrated into forensic practice, measurements should ideally be performed prior to any invasive procedures.

The present findings are consistent with previous reports suggesting postmortem changes in bioelectrical parameters and additionally highlight the confounding effect of autopsy-related manipulation [5–10]. Within the limitations of the present exploratory dataset, phase angle demonstrated the most consistent association with PMI. The exploratory nature of the study and the moderate strength of the observed associations indicate that BIA currently cannot replace established forensic methods and requires substantial additional validation before any practical forensic application can be considered.

Several limitations must be acknowledged. The relatively small sample size restricts statistical power and precludes the development of robust predictive models. Environmental variables such as ambient temperature and humidity were not systematically controlled, and their influence on bioelectrical behavior cannot be excluded. The use of a single-frequency BIA device limits the assessment to global electrical properties and does not allow frequency-dependent analysis of tissue compartments. Nonetheless, these limitations are inherent to pilot forensic studies and do not detract from the methodological and conceptual contributions of the present work. Ambient temperature likely represents a major confounding factor in postmortem bioelectrical behavior, as tissue conductivity, membrane permeability, and fluid redistribution are strongly temperature-dependent phenomena.

The present findings do not support the use of phase angle as a reliable standalone method for PMI estimation. The substantial overlap of values across different PMIs and the marked inter-individual variability indicate that the current approach lacks sufficient discriminative accuracy for forensic application. Rather than validating a new estimation technique, this study primarily demonstrates the complexity and instability of postmortem bioelectrical behavior. The present findings suggest that postmortem BIA parameters exhibit measurable temporal variability; however, the substantial overlap between PMIs currently limits practical forensic applicability.

In conclusion, this exploratory study demonstrates that postmortem bioelectrical parameters, particularly phase angle, undergo measurable changes after death. However, the substantial inter-individual variability, overlap between PMIs, and sensitivity to postmortem manipulations currently preclude reliable forensic application for PMI estimation. The present findings should therefore be interpreted primarily as preliminary observational data highlighting the complexity of postmortem bioelectrical behavior rather than as validation of a novel thanatochronological method.