Background and objective: Postmortem interval (PMI) estimation is an important aim in forensic medicine. An accurate estimation of PMI helps to define the murder time and enable investigators in forensic field especially when they are collecting evidence that can reinforce or exclude the conducts of suspects in a crime. Some techniques were introduced to estimate postmortem interval with the aid of assessment of DNA fragmentation qualitatively and quantitatively. These       include Agarose gel and single cell gel electrophoresis or comet assay. It is recommended to select the most appropriate method to overcome the troubles of postmortem DNA degradation.
Methodology: 30 adult male Sprague Dawley albino rats were selected in the study. Animals were divided into 5 groups and were drowned at the beginning of the experiment. First group's rats had sacrificed immediately after drowning, whilst the 2nd, 3rd, 4th and 5th groups were sacrificed at 6, 12, 24 and 48 hours postmortem respectively. The palatal mucosa and submandibular salivary glands were dissected and extracted for DNA studying and detection. The samples were processed through Agarose gel and single cell gel electrophoresis (comet assay) techniques to estimate the degree of DNA degradation. Results were analyzed statistically and Pearson correlation (r) was used to test the association between PMI & degradation of DNA. Level was considered significant at p value < 0.05.
Results: Agarose gel technique revealed variation in DNA degradation ranging from no changes to severe changes with high correlation association between PMI and DNA in palatal mucosa samples but no correlation in samples of submandibular salivary glands. Comet assay results showed high correlation in all samples from both tissues between PMI and both of tail length and tail moment of the degraded DNA.
Conclusion: Comet assay technique is a more reliable and dependable method in determination of early time of death as shown by the statistical analysis than did Agarose gel electrophoresis technique