A report showing how estimations, calculations, and the tracking of insect activity around a cadaver can be used to accurately estimate the time of death in a number of environmental conditions. Insects have predictable habits, so they are a vital tool in forensic cases such as homicides. This repo...
Introduction
Many factors can affect the estimation of time of death. Most are naturally occurring,
such as insect colonisation and environmental conditions, as well as the known stages of
decomposition. Using this knowledge, it is possible to determine potential human alteration
of a dead body. Perhaps the body was moved? Did a wound speed up the rate of
decomposition? By comparing a victim’s body with another body that has decomposed under
controlled circumstances, tampering of evidence becomes apparent.
Forensic taphonomy and entomology can help determine the conditions that the body
underwent during the postmortem interval (PMI). The application of these areas of study will
be recorded, analysed, and evaluated to determine their worth in a forensic investigation.
Techniques used to record, sample, and analyse taphonomic evidence,
When recording taphonomic evidence, it is important to take photographs/videos of
the body in situ, so that the conditions/location of the body upon discovery can be analysed as
they are as important to an investigation as the body itself.
Upon collection of a body, a total body score (TBS) can be created to give a
numerical value of the level of the body’s decomposition by using the following calculation:
total degradative change = ((total body score of the body) / (total possible score)) x100. The
value from this equation gives the estimated accumulated degree days (ADD) since the time
of death of the body—these values range from 0-3 and are attributed to 4 different parts of
the body (the head, neck, torso, and limbs). A total body score is defined by “characteristics
along a continuous scale” (White, 2016) so that there can be a universal scale for identifying
the TBS. If there is only minor discolouration, then the score would be 0, as decomposition
has only just set in, in that region. A score of 3 suggests that skeletonization has set in, as
well as large portions of soft tissue found missing from the body. A total body score will help
identify the stage of decomposition to determine a time of death and can be carried out
without any equipment, only using visual analysis. As such, a photograph of the body in situ
would be suitable to record the body for later visual inspection if an in-depth analysis of the
exterior and interior cannot be completed.
The Megyesi et al. (2005) method of TBS analysis is the most cited means of scoring
a body’s decomposition. It is completed using three regions of the body unlike the four
described above, which are; “the head and neck, the torso and the limbs” (White, 2016).
When using this method, the scoring system is increased to allow a more accurate range of
results—though this also allows more room for error between investigators. The scores range
from 1-13 for the head and neck: fresh, with no discolouration applies to a value of 1, with
insect activity being applied to 2. Nearer to the end, a value of 12 tells us that bones are
exposed but retain grease, while 13, the highest value of decomposition, tells us that the bone
is dry. The trunk is scored from 1-12, with the same values as the head for 1 and 12, though
the second value for the head and body—insect activity being present—is removed for the
trunk. A value of 2 for the trunk suggests that the skin has become glossy due to bloating and
many small blisters forming on the surface of the skin during autolysis. Finally, the limbs are
assigned values from 1-10, which aim to analyse the severity of colour changes in the limbs
,from 1-5 and the exposure of bone from 6-10. Once added up, this score is recorded and used
to universally represent the visual stage of decomposition of a body. This is then used to give
people not present at a scene a numerical representation of the stage of decomposition.
Collecting bacteria from the gut microbiome and rectum can assist in identifying the
individual, if necessary, but can also link insects to the cadaver as they could have potentially
travelled to the body during the third instar from another nearby cadaver as some larvae have
been reported to travel long distances during their migration from a body. This is typically in
soil and not far from the body, but ensuring that evidence collected is definitely from the
body (like a pre-pupa collected from soil near a body) ensures that the analysis of the insect is
worth the effect and will not skew any estimates of the postmortem interval.
A digital thermometer/data logging device can be used to record the ambient
temperature at a scene. After taking an initial reading of the scene, you may then record the
change in temperature each hour and compare the data collected to that from local weather
towers to validate results if there is any uncertainty. The placement of data loggers can affect
their validity, e.g., “placement of logger in front of windows when measuring indoor
temperatures” (How Are Accumulated Degree Days (ADD) Calculated?, 2021). As such,
care must be taken when choosing the location to record the temperature—one should be
placed near the body, with more in unique locations if multiple loggers are available.
When measuring internal body temperature, a rectal thermometer can be used to get a
quick reading of the body’s temperature. Additionally, an infrared thermometer can take a
fast, though less accurate, reading of the body, which is useful to get a fast reading when
arriving at a scene. Taking a reading of the liver will garner more accurate results as the
temperature will be closer to the core temperature of the body, rather than an infrared or
rectal thermometer, though it requires the body to be damaged. In the past, I have carried out
a test to measure the loss of heat in different sized livers under different conditions. Below is
a graph showing the temperature loss of four different livers under different conditions,
which all have consistent losses of temperature. These results are useful when recording
internal body temperature as they can give an estimated/expected data set for temperature
loss which can be compared to the internal body temperature to estimate ADD/PMI.
, The Glaister equation can be used when an internal body temperature is available to
estimate the hours passed since death. However, this equation assumes that the body loses
1.5℉ per hour, though this value can be replaced if the temperature of the scene is
known—for example, if the body was indoors and air conditioning/heating was at a set
temperature.
98.4 ℉−Internal Body Temperature
1.5 ℉
Results from this equation can be used when questioning alibis, or to credit a
statement given by a witness as, while only an estimate, large discrepancies can highlight
areas of concern in testimonies.
Techniques used to record, sample, and analyse entomological
evidence,
Recording insect activity in and around a dead body is crucial when determining the
PMI as the presence of certain insects and their colonisation can indicate how long the body
has been decomposing as different insects are attracted to the body during different stages.
An example of a highly valuable insect that is typically present on a cadaver is the blowfly
which is one of the first insects present in a body. They are necrophagous, meaning they feast
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