Discussion

The time of death estimation is a crucial part of the forensic investigation. The estimation of an early postmortem interval is based on the compound method by Henssge and Madea [7, 8]. Besides livor mortis, rigor mortis, supravital reactions and pharmacologically induced excitability of the iris, the body core temperature cooling enables the estimation of the time of death [8].

The current gold standard for estimating the time of death based on body core temperature is the Henssge nomogram [4]. Henssge proposed a model for body core temperature cooling under standard conditions, defined as a naked body lying supine on a thermally neutral surface in still air within a closed room without heat sources, which also incorporates corrective factors to estimate the postmortem interval when actual conditions deviate from this standard scenario [4].

In current forensic practice, the time of death estimation is performed manually on-site. This manual calculation can complicate the execution with the Henssge nomogram due to limited practical capabilities at the scene (e.g., darkness, rain, or the absence of a suitable surface for pen-and-paper calculations). Similarly, software-based approaches may also be challenging because using a laptop can be difficult under such conditions and internet access may be limited. Our mobile application facilitates rapid and reliable on-site calculation by enabling simple, one-handed data entry and functioning independently of internet connectivity.

Several software solutions exist to support postmortem interval estimation, each with different capabilities, as shown in Table 2. The software provided by AMASoft [20] integrates the compound method with corrective factors and operates offline; however, it is only available for Windows systems and the full version is not free of charge, which limits accessibility and mobile use. The browser-based calculator available on SwissWuff [21] supports mobile devices and is free of charge, but it requires an internet connection and only provides temperature-based calculations without export functionality. The iTOD App [19] allows temperature-based estimations alongside additional calculations using other factors and can perform calculations offline on mobile devices. However, it only supports English and export functionality is limited to email. In contrast, the mobile application presented in this study integrates the compound method with automated adjustment of corrective factors while remaining freely available

Feature | AMASoft | SwissWuff calculator | iTOD app | ToD application
Temperature-based calculation | Yes | Yes | Yes | Yes
Compound method | Yes | No | No | Yes
Offline functionality | Yes | No | Yes | Yes
Mobile support | No (Windows only) | Yes (browser) | Yes | Yes
Export functionality | PDF export | No | Email only | PDF export
Cost | Not fully free | Free | Free | Free
Languages | German, English | German, English | English | Multiple languages
Additional usability features | Explanatory guidance | - | Explanatory guidance | Explanatory guidance, dark/light mode

When comparing the standard method (Nomogram with case worksheet) with the application-based implementation, the results demonstrate overall excellent agreement, supporting the validity of the application-based calculations. Some deviations were noted in temperature-based calculations, likely due to routine rounding of time values to 15-minute intervals at our institute, which can affect calculations dependent on precise timing. However, both the ICC > 0.99 and the Bland–Altman analyses indicate excellent reliability and minimal systematic bias. Therefore, the two methods can be considered highly consistent and generally comparable, supporting the use of the application-based approach as an alternative to the standard method.

In addition to the computational power to estimate the time of death, our mobile application also automatically identifies any inconsistencies in the entered data. This feature helps detecting inconsistencies on-site, allowing for a direct review and reassessment of the postmortem changes. Our application further operates offline on mobile devices (iOS and Android), provides export functionality in PDF format, and supports multiple languages. Additionally, usability features such as dark and light mode and explanatory guidance were implemented to facilitate practical application in forensic casework.

Accurate determination of the post-mortem interval remains a significant challenge in forensic medicine [32–34]. Methods such as immunohistochemical and histological analyses [37], as well as the incorporation of physiological parameters including body mass index and body surface area, have been proposed to improve the predictive accuracy of time-since-death estimations [35]. In addition, several studies have investigated the use of potassium concentration in the vitreous humor as a biochemical marker for estimating the PMI, providing a complementary approach to the Henssge method [35]. Furthermore, emerging approaches, particularly metabolomics combined with machine-learning techniques for post-mortem intervals exceeding 72 h, represent promising avenues of research [36, 37]. However, the reliability of any predictive tool or digital application ultimately depends on the quality and validity of the established ground truth on which it is based. Defining and validating such reference standards therefore remains a fundamental challenge. Future developments of our mobile application are intended to incorporate emerging research findings that may further enhance its accuracy and practical relevance.