Estimating post-mortem interval using accumulated degree-days and a degree of decomposition index in Australia : a validation study

The development of new and more accurate methods for estimating post-mortem interval (PMI), which can be applied universally, are gaining in popularity. However, given the geographically specific nature of soft tissue decomposition, these methods need to be tested for their accuracy and applicability in a variety of regions before being applied to police and forensic investigations. This study tested two methods for PMI estimations to validate their applicability when used in the Hawkesbury region of New South Wales, Australia. The first method, referred to as the 'Accumulated degree day (ADD)' method, was proposed by Megyesi et al.1 in 2005 and the second method, referred to as the 'Degree of decomposition index (DDI)' method, was proposed by Fitzgerald and Oxenham2 in 2009. Four adult pig carcasses were placed on a soil surface and left to decompose undisturbed from July-September, 2013. The ADD and DDI methods were applied to the remains during this post-mortem interval. Results show that both methods under-estimated the time since death of the remains; however, the ADD method did have the potential to be effective when remains were in the advanced decomposition stages. Failure to validate these methods likely occurred because they could not account for the underlying factors affecting decomposition in this specific environment. An alternative equation was created for these methods, using data collected from the decomposition site in the Hawkesbury region and further validation is being carried out to account for inter- and intra-year variation.