Dr Imtiaz Ahmed Wani
The correct determination of time since death is an important goal in medico legal investigation. Dogmatic application of rules and formulas based upon single and isolated observations is a guarantee of inaccuracy because of the numerous factors of cadaveric or environmental origin that can influence the ‘normal’ rate of postmortem changes. The longer the time since death, the more important the weight of these factors and the more difficult it will be to estimate the death time with some accuracy.
In addition, the precision of the measurements depends on several factors related to the external environment – such as temperature or the exposure or concealment of the body. Other variables include body weight and the presence of wounds or pathologies on the body. Besides gastric emptying time and body temperature estimation in cadaver , focus has been now shifted to biochemical methods that are found to be more accurate since the effect of external conditions is less.
Postmortem succession of human-associated microbial communities (human microbiome) has been suggested as a possible method for estimating postmortem interval for forensic analyses. It is an evaluation of human gut bacterial populations to determine quantifiable, time-dependent changes postmortem. Gut microflora are repeatedly sampled from the proximal large intestine and intestinal bacterial genera are quantified by quantitative PCR / (qPCR) using group-specific primers targeting 16S rRNA genes. Bacteroides and Lactobacillus abundances are used as quantitative indicators of postmortem interval
Microorganisms coexist with us during life, playing an important role in both health and disease. Upon death and as the decomposition process advances, bacterial communities change according to the newly set environmental conditions. The cadavers show similar overall successional changes in oral bacterial taxa as the bodies get decomposed.
The human microbiome, bacteria and other microbes that live on and in our bodies are analyzed, for clues about the postmortem interval of a cadaver. Sampled bacteria from the ear and nasal canals of cadavers through several weeks of decomposition are then analyzed using Next-Generation metagenomic DNA sequencing to determine the identity and abundance of all microbes present. They are scrutinized for the bacterial communities and how they change over time as the bodies decomposed. A statistical model predicts the postmortem interval of unknown samples the degree of accuracy holds through several weeks of decomposition, a substantial improvement over presently available methods.
This microbiome-based method promises a far more definitive method to establish time since death, which could open and close avenues of investigation in homicide cases, shed light upon possible suspects, and corroborate or disprove alibis.
Some proteins disappear very soon after death (such as titin and nebulin), whereas others degrade more slowly (desmin and SeRca1) and some never degrade (a-actin and tropomyosiqin) – at least not within the 240 hours of death .Based on these principles, a method called gel electrophoresis, which can be used to separate proteins according to molecular size , could track a number of proteins according to their sizes over time. A completely new approach for determining time of death which works for up to ten days after death, can be arrived at.
The precision of this approach has been found to be surprisingly high.
Insects play a fundamental ecological role in the decomposition of organic matter. It is the natural tendency of sarcosaprophagous flies to find and colonize on a food source such as a cadaver as a natural means of survival. Sarcosaprohagous fly larvae are frequently encountered by forensic entomologists during post mortem investigations. The maggots of the flies crawling on the dead bodies are widely considered to be just another disgusting element of decay and are not collected at the time of autopsy. They can , however, aid in death investigations (time since death, manner of death and so on).The most relevant colonizers are the oldest individuals derived from the first eggs deposited on the body. The age of the oldest maggots provides the precise estimate of the post mortem interval. With advancement in technology, various new methods have been developed by scientists that allow the data to be used with confidence while estimating the time since death.
Potassium Concentrations in Vitreous Humor
Vitreous humor – the transparent, gelatinous substance that fills the posterior chamber of the eye – is an interesting medium for postmortem biochemical studies owing to its anatomical location and its relative resistance to bacterial contaminations over the first week after death.
.Based on experiments on a large series of cadavers, many authors have established linear relationships between vitreous potassium and time since death. Of the different equations proposed, the most popular are:
•Sturner’s formula: TSD = 7.14 [K+] – 39.1
•Madea’s formula: TSD = 5.26 [K+] – 30.9
where TSD is the time since death (hours)and [K+]is the potassium concentration (mmoll-1).
More advanced methods include DNA quantification, infrared spectroscopy and for buried individuals changes in soils such as the levels of methane, phosphates and nitrates, ninhydrin-reactive nitrogen, volatile organic compounds and water conductivity.
The author is a surgeon specialist at DHS, Srinagar. He can be reached at: firstname.lastname@example.org