Introduction

The compound method by Henssge and Madea is considered the gold standard for narrowing down the time of death in the early postmortem interval. This approach incorporates the temperature-based calculation as well as non-temperature-based criteria concerning lividity, rigor mortis, mechanical and electrical excitability of the skeletal muscle and the pharmacological excitability of the iris [1–5].

Following death, the thermoregulatory processes cease [6]. As a result, the body exchanges energy with its surroundings until it attains thermal equilibrium with the environment [7]. Building on this principle, Henssge established a method for estimating the time of death based on the cooling properties of the body by measuring the core body temperature in conjunction with the environmental temperature, while considering the body weight of the deceased [4].

In addition to temperature-based methods, early postmortem changes such as livor mortis provide important supplementary information. Following cessation of circulation after death, blood flows in the dependent areas of the body under the influence of gravity. The apparent external postmortem discolorations is a consequence of the blood moving into the capillaries of the corium [8]. Initial small spots progressively confluence into larger patches with an increasing postmortem interval [8]. Only in the early stages of postmortem changes, the livor mortis can be completely blanched by thumb pressure and redistributed by repositioning the body which can refine the estimation of the time of death [8, 9].

Rigor mortis is another early postmortem change that develops as adenosine triphosphate (ATP) levels decline, resulting in progressive muscular stiffness. Hereby, the asynchronous stiffening of muscle fibers accounts for both the gradual increase in rigidity and its reappearance following forced joint manipulation [10–12]. Mallach observed that the onset of the rigor mortis manifests within the first seven hours postmortem [9]. Even if disrupted by external force, stiffness can reestablish as additional fibers enter rigor, with full development occurring within the early postmortem period [9, 13].

After death, tissue metabolism does not stop immediately, allowing for postmortem excitation-induced reactions, referred to as supravital reactions [8]. These reactions include the mechanical and electrical excitability of the skeletal muscle as well as the pharmacologically induced excitability of the iris [8]. According to literature there are two phenomena involving the postmortal mechanical excitability of the muscle, “Zsako phenomenon” (up to 2.5 h postmortem) which involves the quadriceps femoris muscle, and “Idiomuscular contraction (bulgur)” (up to 13 h postmortem) which involves the biceps brachii muscle [5, 14, 15]. The electrical excitability of the skeletal muscles represents an additional method for estimating the time of death. Most studies in this domain examined the excitability of the facial muscles, namely the orbicularis oculi and the orbicularis oris muscle [8]. Based on the investigation from Klein and Klein [16], the pharmacologically induced excitability of the iris allows for a temporal narrowing of the postmortem interval, with reported effective time ranges of approximately 3 to 10 h for atropine, 5 to 30 h for tropicamide (Mydriaticum Roche), and 14 to 46 h for acetylcholine. However, some studies showed that measuring the postmortem pupil size limited robustness regarding the time since death estimation [17, 18].

In practice, the estimation of the time since death is typically performed at the scene. Several methodologies currently exist to estimate the postmortem interval. Traditionally, the estimation can be calculated using the nomogram [4] and the integrating chart for casework [5] and corrective factors [2] with pen and paper. Alternatively, various digital tools, such as websites, mobile applications, and software programs, have been developed to assist in calculating these estimates [19–21]. However, no free-of-charge mobile application currently exists that implements the compound method in a comprehensive and integrated manner. We therefore aimed on developing an application called “ToD” that runs completely offline on iOS and Android systems. It provides a comprehensive on-site solution for estimating the time of death based on the compound method, supported by a user-friendly interface and free of charge.