Results

Create a new estimation calculation

Our mobile application named ToD estimates the time of death by analyzing early postmortem changes. The user can assign a unique identification name or number to ensure proper documentation and reference. To comply with privacy and data protection regulations, the naming should not contain any personal identifiable information. Figure 1 displays the home screen of the ToD mobile application along with the process of creating a new case.

Fig. 1: Screenshots showing the home screen of the ToD mobile application: without any cases registered (a), during the registration of a new case (b), and with newly registered cases (c)

A fundamental prerequisite for the accurate estimation of the postmortem interval (PMI) is the precise documentation of the examination date and time. Therefore, the application mandates the input of both parameters at the time of case creation. Since forensic investigations may require modifications or corrections based on additional findings, the recorded date and time of examination remain adjustable.

Once a case is created, all associated data is securely stored locally on the device’s memory, enhancing data security and preventing unauthorized external access. This local storage ensures that the recorded information remains available for subsequent re-evaluation, allowing forensic experts to reassess the input data at any given point in time without relying on external servers or cloud-based storage solutions. Following the creation of a new case, the application enables the input of essential forensic data required for the calculation of the time of death interval, which are explained in the next sections.

Calculating the time of death

Users can freely select or deselect options according to their needs. Inputs that result in contradictory combinations are automatically detected and displayed as an error message in the user interface. In addition, cases in which a calculation cannot be performed, such as when rectal temperature and environmental temperature are too similar to allow a reliable estimation, are likewise identified and displayed to the user via an error message. Explanatory information is provided at selected points where additional clarification may be beneficial. Furthermore, a reset button allows users to restore the temperature inputs to their default values if they wish to start the process from the beginning.

Temperature-based estimation:

The time of death using the body temperature is estimated based on Henssge, which incorporates corrective factors in the calculation [4, 31]. For this purpose, the body core temperature, environment temperature, body weight, and the corrective factor must be entered. The application allows determination of the relevant corrective factors based on the environment conditions at the scene. The corrective factor can be entered directly or selected based on the environment by clicking the calculator icon next to the correction factor field, as shown in Fig. 2. The corrective factor can be selected based on clothing, surface, and environmental conditions. If the corrective factor exceeds 1.4, a body weight adjustment [29] is automatically calculated and the user is informed that this calculation was integrated. If no corrective factor has been chosen, a default corrective factor of 1.0 is used and has no impact on the calculation. Additionally, the user interface integrates an information pop-up for additional support.

Fig. 2: Screenshots displaying the case page of the ToD mobile application: inputting the temperatures (a), selecting the corrective factor based on environmental conditions (b), explanatory text (c)

Non-temperature-based estimation:

Similar to the integrating chart for casework at scene [5], the app distinguishes between “Routine” and “Supplement” examinations.

Within the Routine segment, dropdown menus for “Livores”, “Rigor” and “Electrical excitability” provide structured input options for documenting relevant characteristics (see Fig. 3 for exemplary interface elements). Users can either select between a binary (“YES” or “NO”) response or a multiple-choice response. Options are “Livores Start”, indicating whether livor mortis has begun to develop; “Livores Confluence”, denoting whether hypostatic blood pooling has merged into larger, confluent patches; “Livores Maximum”, specifying whether livor mortis has reached its fullest extent; and “Livores Thumb Pressure”, assessing whether the discoloration completely fades upon the application of localized pressure. Moreover, “Rigor Start”, indicating whether rigor mortis has begun to develop, and “Rigor Maximum”, specifying whether complete rigidity has been achieved. Additionally, the electric dropdown menu allows users to document the electrical excitability of the M. orbicularis oculi by selecting a graded response from I to VI or alternatively choosing “None” if electrical excitability is absent. The reaction for M. orbicularis oris can also be documented with a binary selection.

The supplement section includes the chemical excitability and additional options that work as supplementary input possibilities. The established options for chemical excitability of the iris within the compound methods were added, but with a visual cautionary note since experiments showed misleading results [17]. Additionally, options for mechanical excitability of the M. biceps brachii, allowing users to specify if a reaction of the Tendon Phenomenon or the Idiomuscular Bulge were present. Additionally, for rearrangeability of the corpse, a multiple-choice menu allows the user to specify if the livor mortis remains fully, partially mobile or not rearrangeable at all upon repositioning of the body. For rigor re-establishment, the options allow users to indicate whether rigor reformation has been observed or absent.

Fig. 3: Screenshots showing the case page of the ToD mobile application, where the characteristics of livor mortis (a), rigor mortis (b) and elements of the supplement category (c) can be selected

These structured data entries ensure the standardized documentation of forensic parameters, allowing for a systematic and reproducible assessment of postmortem changes, thereby enhancing the accuracy and reliability of time of death estimation within our application.

The time of death estimation within the application is designed to function dynamically based on the availability of forensic data at the scene. For parameters categorized under “Temperature”, “Routine”, and “Supplement”, the system calculates both a minimum and maximum estimate for the elapsed time since death. Table 1 delineates the specific temporal intervals associated with distinct stages of livor mortis, rigor mortis, the electrical and mechanical excitability of skeletal muscle, and the chemical excitability of the iris, all of which serve as indicators for PMI estimation. Within each parameter category, the lower bound of the estimated interval can only be confirmed or refined by criteria with a higher lower limit, while the upper bound can only be confirmed or refined by criteria with a lower upper limit. In addition to category-specific estimates, the system synthesizes a combined PMI estimate by applying the same constraint-based logic across the categories, thereby generating an interval for the estimated time since death, illustrated in Fig. 4.

Fig. 4: Screenshots showing the calculation of the estimated postmortem interval using all available parameter categories (a) and the error prompt if inputs are contradictory (b)

Technical evaluation

The ICC indicated excellent reliability between both methods for the lower (ICC > 0.99) and upper limit (ICC > 0.98), suggesting a very high degree of consistency in the measurements. The Bland-Altman analysis for the lower limit demonstrated a minimal bias (-0.19), indicating a negligible tendency for the standard method to yield slightly lower values. The limits of agreement ranged from − 1.55 h to 1.16 h, showing a narrow dispersion of differences. For the upper limit, the Bland-Altman analysis showed again a small bias of 0.26, indicating minimal systematic differences. The limits of agreement ranged from − 2.42 h to 2.94 h, demonstrating a tight distribution around the mean and no evidence of systematic deviation.

User experience

The application is designed to enhance user experience through an intuitive and error-resistant interface. If incorrect data is entered or mandatory information is missing, the system generates real-time error messages to alert the user and ensure data integrity. If an incorrect input is provided, the user can negate the selection by re-clicking on the chosen option. Additionally, the application features multilingual support, allowing users to switch between the primary Swiss languages - German, French, and Italian - as well as English, Croatian and Spanish. This functionality ensures accessibility for a diverse user base, facilitating seamless operation across different linguistic regions.

Sharing the calculation results

The application includes an export functionality, allowing both the user-inputted data and the calculated time of death estimation to be generated as a PDF report, as illustrated in Fig. 5. This feature enables forensic investigators to securely store case information for documentation purposes or share it when necessary. The generated PDF can be saved locally for record-keeping or integrated into official forensic case files, ensuring a structured and standardized format for reporting.

Fig. 5: Screenshots displaying the case page of the ToD mobile application, with the resulting time of death estimation shown in the overview table (a) and the generated PDF from the case (b)

App distribution

The application ToD is available for download on both the Apple App Store and Google Play Store, ensuring broad accessibility across iOS and Android devices for forensic professionals. The app is available in the app stores under the name “ToD – estimation”, with the subtitle “Time of death estimation” (Apple App Store: https://apps.apple.com/ch/app/tod/id6744065182?l=de-DE, Google Play Store: https://play.google.com/store/apps/details?id=ch.irm.tod).