A report on the forensic application of decomposition when analysing a cadaver using the 5 stages of decomposition after death and multiple factors that contribute to the increase or decrease in the length of each stage. An evaluation of methods and graphs using practical data are included and disc...
Introduction
The rate of decomposition in a body is effect by multiple variables; the health of the victim, external
factors—such as exposure, and cause of death can help determine the post-mortem interval (PMI), which is
the elapsed time since death.
As the body begins breaking down and becoming home to different insects, which are studied under
the term forensic entomology, along with analysing the decay of the body, studied under taphonomy. These
two fields utilise the biological evidence of human remains, and a thorough analysis and discussion is
necessary to determine their worth in a forensic investigation. Additionally, the strengths and weakness of
relying on these techniques will be evaluated to ensure that the evidence gathered is valuable enough to
warrant the time spent.
Stages of decomposition
There are five general stages during decomposition that can indicate the time and cause of death.
Under set conditions these processes would consistently occur, making them an important source of natural
information for determining the post-mortem interval and assessing external factors that might have sped up
or slowed down the rate of decomposition.
The word ‘taphonomy’ is used to cover the study of post-mortem decay of a dead body in forensic
investigation.
Stage 1
Autolysis
This stage begins almost instantly after death. Initially, there are few signs of external
decomposition, though small blisters do begin forming on the surface of the skin. Internally, the body’s pH
begins to change due to the lack of oxygen in the body. This causes cells to lose their structure and release
enzymes which begin the self-digestion of the body.
It is during this period of around 3 days that blow flies, flesh flies, and bluebottle flies are attracted to
the body. As the insects’ main way of locating the body is smell, this can be affected by exposure. Though it
is extremely helpful to be able to analyse the flies present as the insect succession (their lifecycle) can help
accurately indicate the time of death.
Pallor-mortis
The word ‘pallor’ describes the pale, sickly appearance of the skin, and the word ‘mortis’ mean
death. This process occurs around 20 minutes after death.
Pallor-mortis occurs because of the deprivation of oxygen, stopping the blood flowing throughout the
body, and causing the skin to lose its reddish sheen and take on a pale, lifeless appearance. Additionally, the
cornea will begin forming a cloudy layer which becomes increasingly opaque during the next 24-48 hours,
making this another supporting method in determining the post-mortem interval.
Algor-mortis
The word ‘algor’ means coldness and describes the loss of body temperature post-mortem. This
process begins roughly one hour after death and continues until all body heat is lost, which depends on
numerous factors, such as the external temperature, exposure, and body fat, along with the type of wound
and clothing. Under set conditions, however, the body will lose temperature at a standard rate that can be
measured by a curve on a graph.
Rigor-mortis
The word ‘rigor’ means stiffness. This process occurs when muscles in the body begin to stiffen,
which happen about half-a-day to a day post-mortem. Smaller muscles are affected first and they continue to
stiffen for up to three days in total. This stiffing occurs “due to a range of chemical changes in the muscle
structure.” (Rigor Mortis - an overview | ScienceDirect Topics, 2021).
, Livor-mortis
The word ‘livor’ means bluish colour. Livor-mortis describes the pooling of remaining blood in the
body due to gravity and lack of circulation throughout the body. The process begins just minutes after death
causing increasingly dark patches to form on the skin where the body is lowest to the ground.
Stage 2
Bloat
The bloating of the body, caused by the building-up of gases in the abdomen, is the first visible sign
of decay, as well as the possibility of the skin forming a marbled appearance—this is caused by an
“outlining of the superficial blood vessels,” (Shedge, Krishan, Warrier and Kanchan, 2021).
During this stage, the body may increase almost twice in size. Additionally, the internal gases formed
by bacteria produce a rancid smell, called putrefaction, that acts to tell nearby animals that the person is
dead.
Insects such as carrion beetles come to feed on the fly larvae planted in the body as well as the soft
tissue within 4-7 days. In terms of simply determining the insects present at a glance without further
investigation, beetles are one of the more important insects’ presence to validate as they typically wouldn’t
be interested in a body just after death like a blow fly or flesh fly would be. Furthermore, most flies still take
interest in the body until skeletonization occurs, so their presence would not necessarily indicate time of
death without further investigation.
Stage 3
Active decay
Now that the body has bloated it begins to deflate, releasing all the internal gases. As the body’s soft
tissue begins to decompose, they become liquified and are released, along with other internal fluids, through
any available orifice, which indicates the beginning of this third stage of decomposition.
Because of the liquification of the internal organs and muscles, the body loses most of its mass
during this stage. However, bits of hair, bone, cartilage, along with nails, remain.
Ants and cockroaches begin to take interest in the cadaver after a week, once the bloating stops and
the decay begins as they are attracted to the release of internal gases and the now-liquid organs and skin are
easier to consume.
Stage 4
Advanced decay
This is the final stage before skeletonization, where the remaining skin becomes hard and leathery,
and the bone starts to become exposed.
During this late stage of decomposition, certain beetles that were not interested in the body earlier
begin to arrive. Ham & Checkered beetles pray on other flies and beetles and join the skin beetles in feeding
on the dead tissue.
Stage 5
Skeletonization
At this point, most of the flesh has been removed and all that remains is the skeleton. This stage is
reached anywhere from a week to four weeks post-mortem as it is heavily influenced by the environmental
conditions the body is in. It’s worth noting as well that bones may become loose and roll away from the rest
of the skeleton depending on the state that the body is left in.
While the only physical articles that remain are the bones and teeth, butyric acid can cause a cheese-
like smell to persist after putrefaction.
External factors
Anything that would not happen under set conditions, such as an increase/decrease in temperature,
infections, or predators, are ‘factors’ that can increase or decrease the rate at which a body decomposes. For
example, an infection may attract certain insects that would not normally be present—or perhaps not so
early—to a body, which would increase the rate at which active decay begins, and thus skeletonization.
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