Post-Mortem Examination, Post-Mortem Changes and Time Since Death

A medico-legal post-mortem in India runs on a standard workflow the syllabus expects you to list in order. Legal authorisation comes from the police officer-in-charge under BNSS 2023 Section 194 (which replaced CrPC Section 174 from 1 July 2024) for suspicious or unnatural deaths, or from a Judicial Magistrate under BNSS Section 196 for custodial and dowry deaths. The investigating officer issues a written requisition with the inquest report (panchnama) and identification particulars, and the body goes to a government mortuary with police escort.

Identification in the mortuary checks the body against the inquest paper for tag, constable's signature and physical description (sex, age, height, clothing, ornaments, moles, scars, tattoos), attested by two witnesses. External examination is done before the body is washed: general condition, clothing, post-mortem changes, and every injury with shape, size, site, edges, depth and age, photographed in plain view and with scale per the forensic photography rules used at the scene. Internal examination follows the three-cavity sequence (head, thorax, abdomen) using I-shaped, Y-shaped or modified Y incisions; each organ is weighed and sectioned.

Sample collection drives toxicology and serology. Standard viscera in poisoning cases are stomach with contents (about 200 g), small intestine with contents (about 30 cm), liver (about 200 g), half a kidney, blood (10 to 15 mL) and urine, sealed in saturated saline or rectified spirit for non-volatile poisons; sodium fluoride plus potassium oxalate is added to blood for alcohol estimation. Each sample sits in a separate sealed container listed in Form 21 (viscera receipt) which travels to the FSL with the

The three primary post-mortem changes are the immediate signs the examiner records at the body. Read together they fix the first 24 hours of the PMI in most cases.

Algor mortis (body cooling). Once circulation stops the body loses heat by radiation, conduction and convection. Under temperate Indian indoor conditions the rate is roughly 0.7 to 1 degree Celsius per hour for the first few hours, then slower toward ambient. The classical rule of thumb (now superseded by the Henssge nomogram in Section 4) is PMI (hours) approximately equal to (37 minus rectal temperature) divided by 0.93. Cooling is delayed in obese, fevered or heavily clothed bodies and high ambient temperature; faster in lean bodies, children and cold environments.

Livor mortis (post-mortem hypostasis). Blood, no longer pumped, settles by gravity into dependent capillaries. Bluish-purple discoloration appears in dependent parts with pallor in pressure areas. Onset 30 minutes to 2 hours, fully developed 6 to 8 hours, fixed by 8 to 12 hours. Before fixation it blanches on pressure and shifts if the body is turned; after fixation it does not. Colour is a cause-of-death pointer:

• Cherry-red (pink): carbon monoxide (carboxyhaemoglobin), also cyanide and refrigerated bodies.
• Brown: methaemoglobinaemia (nitrites, aniline, potassium chlorate).
• Bluish-black or deep purple: asphyxial deaths.
• Greenish: hydrogen sulphide poisoning.

Rigor mortis (post-mortem stiffening). ATP runs out and actin-myosin cross-bridges lock. Onset 1 to 2 hours, full development 8 to 12 hours, persists 12 to 24 hours, passes off 24 to 36 hours under average Indian conditions. Nysten's law: rigor appears first in involuntary muscles (heart, diaphragm), then face (eyelids, jaw), neck, trunk, upper limbs and lastly lower limbs; it passes off in the same order. Faster in muscular subjects who exercised before death, in hot environments, and after strychnine or pilocarpine death; slower in cachectic subjects and cold environments.

Once rigor passes off, secondary changes take over. NTA favours the time order and the environmental conditions that drive each pathway.

Decomposition combines autolysis (self-digestion by released intracellular enzymes, earliest in pancreas, gastric mucosa and adrenal medulla) with putrefaction (bacterial breakdown, mainly by Clostridium welchii and gut flora). The visible sequence in temperate Indian conditions:

• Greenish discoloration over the right iliac fossa (caecum sits there): 12 to 24 hours.
• Spread of green to whole abdomen, chest and thighs: 24 to 36 hours.
• Marbling (greenish-black branching over superficial veins, haemoglobin plus H2S): 24 to 48 hours.
• Gas distension and bloating with protrusion of eyes and tongue and purge from mouth and nose: 48 to 72 hours.
• Skin slippage, blisters, hair and nail loosening: 3 to 5 days.
• Liquefaction of soft tissues, skeletalisation with scavenging: weeks to months.

Putrefaction is faster in hot humid climates (Casper's dictum: 1 week in air = 2 weeks in water = 8 weeks in soil). In Indian summer plains the timeline compresses: marbling and bloating by end of day one is common.

Adipocere (saponification). In moist, anaerobic conditions (water-logged grave, septic tank, well, monsoon-flooded paddy), body fat hydrolyses to saturated fatty acids (palmitic, stearic, oleic) plus calcium and magnesium soaps, producing a greasy, waxy, yellowish-white substance that preserves contour and features. Begins in subcutaneous fat (cheek, breast, buttock, abdomen) at about

The qualitative changes in Sections 2 and 3 give wide brackets. Quantitative methods are used to narrow the PMI window.

Body cooling, Newton's law and the Henssge nomogram. Newton's law of cooling in post-mortem form is Tt = Te + (T0 minus Te) e^(minus k t), where Tt is rectal temperature at time t, Te is ambient, T0 is body temperature at death (37.2 degree C), and k is a cooling constant. The real curve is sigmoidal: a plateau of 30 minutes to 3 hours, a near-linear fall, then a slow tail. The Henssge nomogram (Claus Henssge, 1988) is the modern global standard: it takes rectal temperature, ambient temperature, body weight and a corrective factor (clothing or cover, still or moving air, dry or wet body) and gives PMI with a 95 percent confidence band of about plus or minus 2.8 hours under standard conditions.

Vitreous humour potassium (Madea and Sturner). Potassium leaks from retinal cells into the vitreous at about 0.19 mEq per L per hour. Sturner (1963): PMI = 7.14 times [K+] minus 39.1. Madea (1989): PMI = 5.26 times [K+] minus 30.9. Useful from a few hours up to about 120 hours, and less affected by ambient temperature than skin or rectal temperature, a favourite NET MCQ. Less reliable in young children, after long agonal states and in deranged ante-mortem electrolytes.

Gastric content and bladder fill. The stomach empties light liquid meals in 1 to 2 hours, mixed meals in 3 to 4 hours, heavy fatty meals in 4 to 6 hours. Recognisable food items (rice grains, dal, vegetables) read against the last known meal narrow the PMI. An empty bladder at night-time death suggests early morning after voiding; a full bladder suggests death during sleep.

Past day five, three adjunctive method families take over.

Forensic entomology. Blowflies (Calliphoridae) locate a fresh body in minutes and oviposit on orifices and wounds. The first wave in India is dominated by Chrysomya megacephala, Chrysomya rufifacies and Lucilia cuprina; later waves bring flesh flies (Sarcophagidae), beetles (Dermestidae, Silphidae) and mites. PMI uses developmental age of the oldest larvae (egg, instar I, II, III, prepupa, pupa, adult) read against accumulated degree-hours, plus insect succession for older remains. Full method at the sibling topic on forensic entomology and insects of forensic importance.

Forensic anthropology decomposition stages. The standard five-stage scheme: fresh (0 to 2 days), bloat (2 to 7 days), active decay (1 to 3 weeks, maggot mass activity, big biomass loss), advanced decay (weeks, drying tissue, beetles), dry or skeletal (months to years). Calibrated to local climate; Tennessee Body Farm is the global reference, Indian field data is being built at NFSU Gandhinagar and AIIMS Delhi.

Scene and circumstantial pointers. A dated newspaper, undelivered courier, stopped watch, uneaten meals, mobile-phone last activity and CCTV last sightings all narrow the PMI window and must be read with body findings, not in isolation.

The BNSS 2023 reform is the single biggest statutory change examiners now test on. BNSS Section 194 (in force 1 July 2024) replaced CrPC Section 174 as the police inquest; BNSS Section 196 replaced CrPC Section 176 as the magistrate inquest (custodial deaths, police firing, dowry deaths within seven years of marriage, deaths of women in suspicious circumstances). The substantive workflow is unchanged, only the section numbers.

The MoH&FW Standardized Autopsy Protocol (2021) is the national template. AIIMS Delhi Department of Forensic Medicine, KEM Mumbai, GMC Trivandrum, JIPMER Puducherry and PGI Chandigarh are the named reference centres in PSC and NET questions. NFSU Gandhinagar publishes Indian PMI data sets. Modi's Medical Jurisprudence and Toxicology (26th edition, edited by Krishan Vij) and Reddy's Essentials of Forensic Medicine and Toxicology remain the two most-cited Indian textbooks.

Form 21 (viscera receipt) is the prescribed form that signs every handover of preserved viscera from mortuary to constable to FSL, giving the chain of custody record the defence will probe. Mismatches between Form 21 and container seals are the single most common reason for BSA 2023 objections in poisoning trials. The full police-to-court flow is covered in Bharatiya Nagarik Suraksha Sanhita investigation.

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