Introduction

The estimation of the postmortem interval (PMI) represents a cornerstone of forensic investigation and continues to be one of the most methodologically complex and scientifically challenging tasks in legal medicine [1–3]. Despite decades of research and the development of multiple thanatochronological approaches, the determination of time since death remains burdened by intrinsic biological variability, environmental interference, and methodological constraints that limit both accuracy and reproducibility [2–4]. Traditional methods based on early postmortem phenomena, including algor mortis, livor mortis, and rigor mortis, are primarily applicable within narrow temporal windows and are significantly influenced by ambient temperature, body habitus, clothing, and pre-existing pathological conditions. Similarly, biochemical, molecular, and entomological techniques, although valuable in specific contexts, often require specialized expertise, extended processing times, or assumptions that restrict their routine forensic applicability [5].

In this framework, there is a growing demand for objective, quantitative, and operator-independent methods capable of capturing postmortem biological changes through measurable physical parameters. Instrumental approaches that rely on standardized acquisition protocols and yield reproducible numerical outputs are particularly appealing, as they offer the potential to reduce subjective interpretation and inter-observer variability. Among these techniques, Bioelectrical Impedance Analysis (BIA) has emerged in clinical medicine as a robust and extensively validated tool for the assessment of body composition, hydration status, and cellular integrity, yet its application in forensic thanatochronology remains largely unexplored [6, 7].

BIA is based on the transmission of a low-intensity alternating electrical current through biological tissues and the measurement of the resulting opposition to current flow, which is determined by the conductive and capacitive properties of the body [8, 9]. Electrical resistance reflects the conductive behavior of ionic solutions, primarily influenced by total body water and electrolyte distribution, whereas reactance arises from the capacitive effect of cell membranes and tissue interfaces, which temporarily store electrical charge. The combination of these two parameters yields impedance, while their angular relationship is expressed as the phase angle. In vivo, phase angle is widely regarded as an indirect marker of cellular health and membrane integrity, with lower values typically associated with cell membrane breakdown, fluid imbalance, and poor clinical outcomes.

The postmortem environment, however, differs fundamentally from the living state, as it is characterized by the cessation of active cellular regulation and the predominance of passive physicochemical processes. Following death, progressive loss of membrane permeability control, collapse of transmembrane ion gradients, redistribution of intra- and extracellular fluids, and early autolytic phenomena are expected to alter tissue conductivity and capacitance in a time-dependent manner. These processes, which evolve continuously during the postmortem interval, provide a theoretical basis for the use of bioelectrical measurements as potential indicators of PMI. Nevertheless, the directionality and temporal behavior of individual electrical parameters after death cannot be directly inferred from in vivo models and require dedicated experimental investigation.

Preliminary forensic studies have suggested that bioelectrical parameters may exhibit systematic variations in relation to PMI, indicating that BIA may provide measurable postmortem electrical changes whose forensic significance remains uncertain [6, 7]. However, available evidence remains limited, and several critical aspects have yet to be clarified. In particular, the behavior of the phase angle in the postmortem period appears to diverge from established clinical patterns, raising questions regarding the underlying mechanisms governing postmortem electrical changes [10, 11]. Additionally, the potential influence of confounding factors such as body mass index (BMI), cause of death, comorbidities, and invasive postmortem procedures has not been comprehensively evaluated, hindering the development of standardized interpretative models.

BMI was explored as a potential source of inter-individual variability in bioelectrical measurements. However, given the exploratory nature of the study, no specific assumptions were made regarding its relationship with postmortem interval.

Against this background, the present study aims to provide an experimental evaluation of the postmortem application of Bioelectrical Impedance Analysis in a series of 29 human cadavers. By systematically analyzing resistance, reactance, impedance, and phase angle in relation to PMI and BMI across a wide temporal range, and by assessing the effect of autopsy-related anatomical disruption on electrical parameters, this investigation seeks to clarify the feasibility, behavior, and forensic relevance of BIA-derived measurements. The objective of the present exploratory study was to characterize the postmortem behavior of BIA-derived parameters across different PMIs rather than to establish a predictive PMI estimation method.