Estimating postmortem interval for human cadavers in a sub-tropical climate using UV-Vis-near-infrared Spectroscopy

Estimating postmortem interval (PMI) of surface found skeletal remains is challenging. This novel study used UV-Vis-NIR spectroscopy to scan soil collected from cadaver decomposition islands (CDIs) ranging from 15- to 963-d postmortem and control soils. A decomposition product spectra model (DPS model) was constructed by deducting the control soil spectra from the CDI soil spectra for the estimation of postmortem indices: PMI (d), ADD₄ , ADD₁₀ , and ADD₂₀ . The DPS model (n = 55) was calibrated and subjected to a full cross-validation. Calibration R² and RPD for the DPS model ranged from 0.97 to 0.99 and from 6.1 to 9.9, respectively, for the four postmortem interval indices. Validation R² and RPD for the DPS model ranged from 0.73 to 0.80 and from 1.9 to 2.2, respectively. The DPS model estimated postmortem intervals for three test CDIs in a clay soil under perennial grassland (test set 1; n = 3) and six CDIs in a sandy soil under a loblolly pine forest (test set 2; n = 6). Test set 1 had PMI prediction ranges from -69 to -117 days, -796 to +832 ADD₄ , +552 to +2672 ADD₁₀ , and -478 to -20 ADD₂₀ of observed PMI. Test set 2 PMI prediction ranged from -198 to -65 days, -9923 to +2629 ADD₄ , -6724 to +1321 ADD₁₀ , and -2850 to +540 ADD₂₀ of observed PMI. Test set 2 had poor predictions for two CDIs, for all measures of postmortem indices resulting in discussion of sampling depth, effect of body mass index (BMI), and scavenging.