Estimation of the time since death based on body cooling: a comparative study of four temperature-based methods

The estimation of the time since death is an important task in forensic medicine that mainly relies on body cooling in the early post-mortem period. The rectum has been traditionally used to determine the central core temperature after death, though the external auditory canal has been proposed as an alternative site by several authors. The objective of this study was to assess the ability of four body temperature-based methods (Henssge’s rectal nomogram, Henssge’s brain nomogram, and Baccino’s both interval and global formulae based on ear temperature) to estimate the post-mortem interval (PMI). PMI calculations were carried out based on ear and rectal temperature measurements performed with a reference metal probe on 100 inpatient bodies with an average PMI of 4.5 ± 2.5 h. For practical purposes, ear temperature measurements were applied to Henssge’s brain nomogram. All methods could be applied to 81 cases, since high body temperatures prevented the rectal nomogram method from being used in most of the remaining cases. The actual PMI was within the time interval (95% CI) provided by the rectal nomogram method in 72.8% of cases, and in 63.0% to 76.5% of cases when using ear temperature-based methods. The proportions of adequate estimates did not differ statistically between the different methods. When the methods failed to provide a reliable time interval, all except the brain nomogram tended to underestimate the PMI. Similar results were obtained in the subgroup of normothermic patients at the time of death (n = 63), confirming that the PMI calculations had not been biased by the inclusion of patients with thermoregulation disorders. Our findings are in accordance with the published literature which suggests that ear temperature-based methods are as reliable as those based on rectal temperature for estimating the early PMI and that they may be used as quick, simple, and non-invasive methods at the scene, although caution should be taken in interpreting their results given their high error rates. However, further research including field studies is recommended to confirm their practical relevance in forensic casework.