Post-Mortem Interval (PMI)

By @forensicfield

Many types of changes to a body occur after death. Some of those that can be used to determine the post-mortem Interval are –

  • Change In The Eye
  • Algor Mortis
  • Hypostatis
  • Rigor Mortis
  • Putrefaction
  • Adipocere
  • Mummifiication
  • Stomach & Intestinal Contents
  • Skeletonization
  • Insect Activity
  • Contents Of Urinary Bladder
  • Bone Marrow Changes
  • Circumstantial Evidence

Changes can also differentiate in following stages:-

The changes which take is may be helpful in estimation of the approximate time of death and the sign of death appear in the following order :-

I.     Immediate Changes

  1. Insensibility
  2. Cessation Of Respiration
  3. Stoppage Of Blood Circulation

II.     Early Changes  

  1. Loss Of Elasticity
  2. Change In The Eye
  3. Algor Mortis
  4. Flaccid Of Muscles
  5. Postmortem Lividity
  6. Livor Mortis

III.    Late Changes

  1. Putrefaction
  2. Adipocere Formation
  3. Mummification

STAGES OF DECOMPOSITION OF BODY 

These Stages Of Post-Mortem Changes Are::

Stage 1 – Fresh Stage
Stage 2 – Bloated Stage
Stage 3 – Active Decay Stage
Stage 4 – Post Decay Stage
Stage 5 – Skeletonization

Fresh Stage

This stage starts from the moment of death to the first signs of bloating of the body. The first organism to arrive are the blowflies (Calliphoridae).

Livor mortis

Cessation of circulation and loss of muscles tone after death allows blood within vessels to settle under gravity, producing a pink or purple colour in those areas of the body that are lowest or dependent.

Hypostasis  was maximal /  fully developed after about 12 hours.

Rigor mortis

  • Rigor mortis is a temperature dependent physiochemical phenomenon that occurs in muscle cells following cessation of a supply of oxygen.
  • Rigor mortis develops at the same time through out the body, but it is detected more rapidly in small muscles such as around eyes and mouth.

Algor mortis (post mortem body cooling)

A Body Cools After Death According To Old Rule. Body Temperature Falls By 1.50F (210C) Per Hour. The Rate At Which A Body Cools After Death Depends On The Following-

  • Mass Of The Body,
  • Surface Area Of The Body,
  • Body Temperature At The Time Of Death (370C Is Used As Expected Temperature),
  • Site Of Reading Of Post Mortem Body Temperature,
  • Posture Of The Body,
  • Clothing And Coverings,
  • Obesity (Fat Insulates),
  • Emaciation,
  • Environmental Temperature.

Bloated stage

Breakdown of the body continues because of bacterial activity, or putrefaction and this is the easiest stage to distinguish. Gases causing the corpse to bloat are generated through metabolism of nutrients by anaerobic bacteria.

Initially the abdomen swells but later the whole body becomes stretched like an air- balloon.

At this stage more and more blowflies are attracted to the body, possibly in response to the smell of the breakdown gases.

Active Decay Stage

This stage is recognizable by the skin of the corpse breaking up and starting to discard from body.  The removing of skin allows the decomposition gases to escape and so the inflation of the body gradually subsides as putrefaction continues.

Decomposition / Putrefaction

Dead Bodies Are Eventually Breaking Down Into Their Constituents Components.

Soft Tissues Degrade And Liquefy Over A Period Of Time, The Rate Of Progress Of Which Is Temperature Dependent. The Warmer The Environment In Which The Body Lies, The More Rapid Liquefaction Occurs.

Dead Bodies Degrade At Different Rates Depending Upon The Medium In Which They Are Placed- Immersion In Water Slows The Process, While Burial Slows The Rate Even More.

Mummification

When a body lies in dry condition it may desiccate instead of putrefying, a process called mummification.

Mummified are dry and leathery and often brown in color.

Mummification commonly occurs in warm and hot climates, such as desert.

Post-Decay Stage

In the later stages of decay, all that remains of the body are skin, cartilages and bones with some remnant of flesh including the intestines.

Any remaining body tissue can be dried. The biggest indicator of this stage is an increase in presence of beetles and a reduction in the dominance of the flies (Diptera) on the body.

Skeletonization

The Loss Of Soft Tissues Results In Skeletalisation. At This Stage Of The Body Is Only Hair And Bones.

It May Take Years For A Body To Become Skeletonized When Buried But Weeks In Warm Climates Where The Body Has Been Exposed To Predation.

The Body Has Clearly Reached Its Final Stage Of Decomposition.

:: Note ::

In Water These Stages Still Same With An Additional Stage Which Is Floating Decay Stage, Where The Body Rises To The Water Surface.

At this point, besides aquatic insects such as chironomid larvae and invertebrates such as water snails, terrestrial insect species also colonize the body.

Saponification

Bodies exposed to action of water or buried in damp, moist soil are opt to undergo certain changes in the course of which they become saponified and the formation of a substance known as adipocere is the result.

Adipocere

If The Body Is In An Environment Which Combines A High Humidity With High Temperatures, The Subcutaneous Body Fat Of The Face, Buttocks (Breasts In The Female) And The Extremities Become Hydrolyzed. Fatty Acids Are Released. These Form Food For Bacteria, Which Can Speed Up The Rate At Which Adipocere Is Made.

Succession

Investigating post-mortem interval for a period of at least 3 or more months may mean that there is a large assemblage of flies, beetles and other insects present on the body. These can be use for the calculation of PMI using another method. This method requires that first of all every specimen identified to their family. After that an attempt is made to relate this ‘snapshot’ of decomposition fauna to the succession of insects which routinely colonize a corpse at that site knowing which insects are present and which are absent locally in what season help the entomologist to estimate the PMI.

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