Unit 4 - Forensic Investigation Procedures in Practice
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Analytical techniques to examine forensic evidence collected from a simulated crime scene
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Unit 4 - Forensic Investigation Procedures in Practice
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PEARSON (PEARSON)
Learners should produce a portfolio of laboratory examination forms, including drawings and photographs where appropriate, method sheets and results of analysis. This should be supported with an observation document, completed by the assessor.
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Unit 4 - Forensic Investigation Procedures in Practice
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Use of analytical techniques to examine forensic evidence from a simulated crime scene
Examples of typical analytical techniques
Biological:
Blood / bodily fluids
Blood and bodily fluids are examined through presumptive and confirmatory testing, which
can then lead to blood being tested in DNA profiling. Presumptive testing doesn’t confirm if a
sample is blood, rather it helps to suspect if it is blood.There are many ways to carry out
presumptive testing, most commonly, the Kastle-meyer test. This type of testing involves the
swabbing of the evidence area using a cotton swab, placing the sample into a test tube of
distilled water and shaking it lightly. After shaking the sample, add a few drops of
Phenolphthalein to the test tube, followed by a few drops of hydrogen peroxide. Positive
Kastle-Meyer testing turns the sample/cotton swab a vibrant pink colour, if the sample is a
negative test there will be no colour change.
The presence of haemoglobin and phenolphthalein react with hydrogen peroxide to produce
a vibrant pink colour. Haemoglobin (found in blood) results in the pink colour of the sample,
resulting in it to be a positive presumptive testing.
Confirmative testing provides a definite conclusion that the sample contains biological
materials.
A common confirmatory testing of blood is the Takayama test, also known as the
Hemochromogen test. The following reagents are used to carry out the Takayama test;
saturated glucose solution, sodium hydroxide (10%), pyridine, and water. To carry out the
test, pour 5 ml of saturated glucose solution into a beaker, then add 5 ml of sodium
hydroxide. Mix the solution and then add 5 ml of pyridine solution, again mix thoroughly, then
add 10 ml of distilled water to the beaker and again mix all the reagents together. After,
scrub the dried possible blood sample, and put it over a glass slide. Once put over a glass
slide, add 3 drops of the Takayama reagents, then cover the sample with a coverslip and
observe under a microscope.
A positive result should appear within six minutes, a visible formation of feathery crystals
should be seen with a pinky / red colour. The crystals should appear in clusters in large
amounts. This means the sample is confirmed as blood. A negative result will result in no
feathery crystals forming within 30 minutes of the testing, this means the sample is not
blood.
A common confirmatory test is the RSID testing of human blood. The way the test is carried
out is by adding blood to a lateral flow strip, the use of two antibodies detects the presence
of human glycophorin A, this is found in human red cell blood cell membranes. Applying the
antibodies to the sample, will lead to specific markings which indicate if the test was positive
or negative. The markings appear because they are the areas where the antibodies are
located, therefore appear when tested with blood. This type of testing has its downsides, it
,often produces inaccurate results if the blood had been treated with luminol. When the test is
carried out properly, it produces highly reliable results. A benefit of RSID testing is that it is
highly versatile to test for other human bodily fluids.
Another type of blood analysis is through blood grouping. This type of testing confirms the
blood type of the person's blood. Although it does not connect the blood to who the individual
is, rather it confirms their blood type. Often, blood grouping is carried out when individuals
have blood transfusions. This determines which of the blood donors blood can be used with
which patient. In forensic analysis, it helps narrow down information as to whose blood was
found at the crime scene. Individuals with blood group A, have A antigens on their red blood
cells, they also have anti-B antibodies in their blood serum. Person’s with blood type B will
have B antigens present, the body’s antibodies react with incoming B antigens and the blood
will clot. Individuals with A blood type have A and B antigens on their RBC’s, there are no
antibodies present in their blood, as a result, they can accept both A & B antigens.
Individuals with blood type O have no antigens on their RBC’s. Forensic blood typing
analysis determines the antigens present on the RBC surface of sampled blood, it identifies
the blood group of the blood found at the crime scene.
The serological technique consists of testing antibodies and antigens present in the
samples. Antibodies are produced as an immune response to antigens, binding to specific
antigens to prevent illness. A & B antigens and antibodies are used to analyse the ABO
blood group. By adding a small quantity of blood tested with anti-A antibody serum, if A
antigens are present, the antibodies will bind. The cells would clump together, causing a
visible cloudy precipitate to form in the sample, this is a positive result for that specific
antigen. The sample can then be tested for the presence or absence of B antigens and
anti-Rhesus antigens.
Fingerprints
Every person's fingerprint is unique to themself, no person has identical fingerprints and as a
result make a huge impact if the print can be allocated to a suspect. By examining the
personalised characteristics of fingerprints, an exact match can be found as to whose prints
they are. Modern day advances in fingerprint analysis allows us to use the national
automated fingerprint identification system, this digitally compares the fingerprint to ones
known on file, this can dramatically speed up the identification process of these fingerprints.
The digital files will highlight characteristics such as whorls, loops and arches. These are
what make the fingerprint unique. By comparing the placement of these characteristics to
,ones on file, a match can be made. Using the fingerprint identification system has some
limitations, most of the fingerprints on file would be from persons who previously have
committed a crime or have had a fingerprint sample taken. If the person whose fingerprints
were found hadn't committed a previous offence, their fingerprints wouldn’t be found on the
database. As a result, there are some limitations to the online databases. If the fingerprints
aren’t found, a fingerprint analyst will examine the prints using a magnifying glass. They will
identify all the unique characteristics of the fingerprint (they must highlight 16 qualities). The
fingerprints will also be compared to the suspects prints to confirm if a suspect left the
fingerprints at the crime scene. Unless a match has been confirmed, the fingerprints will be
used in court but cannot be used to match an individual to the crime.
Hair
Analysing hair is very helpful in identifying if its human or animal, it determines the possible
location of where the hair came from, if the hair had been removed by force and additionally,
the root of the hair strand can be used in DNA profiling.
An example of hair analysis is through microscopic analysis of the hair strand. To carry out
this type of analytical technique, observe the structure of the hair under the microscope,
locate specific characteristics of the hair such as pigmentation, size and structure of the
medulla. Microscopic analysis, mainly, is used to determine if the sample is human or animal
hair. Human hair and animal hair have different features. In human hair, the medulla of the
hair will be fragmented or interrupted. Whereas the medulla in animal hair is continuous. The
human hair has the natural pigmentation of the hair, unless it is dyed, will be continuous.
Animal hairs have radical colour / pigmentation throughout the hair. The shape of the root in
human hair is a club shape, whereas in animal hair, the root is dependent on the species.
Another analytical technique for hair analysis is mitochondrial DNA analysis. After a cell dies,
the mitochondrial DNA can still be detected, even if no root is attached to the hair. Therefore,
this type of analysis can be used in DNA profiling, to link the hair to an individual.
Analysis of hair follicles can help determine the ancestry and race of the individual.
Additionally, another factor that can be discovered from hair analysis, is the location of where
the hair came from on the body. Hair follicles on different parts of the body have different
textures, hair from the scalp is soft in texture, often has split ends at the base and has a
, moderate shaft size, pubic hairs are coarse and have a wiry texture, they are considerable
thicker than strand of hair from a person's head. Determining the location of where the hair
came from on the body can suggest if there was possible resistance from the victim,
possible sexual assault and even it can determine the force at which the hair was removed
from the body.
Skeletal material
Skeletal material can be analysed to discover the identity of the skeleton and can also be
markings left on the body to indicate the cause of death.
To begin the analysis of remains, anthropologists have to determine if the remains are
human or animal. In animal and human bones, osteons are present. They carry blood supply
in the body. To differentiate between human and animal remains, anthropologists examine
the osteons in the bones under a microscope. There is a visible difference between human
and animal osteons. Osteons in humans are sporadically placed around the bone, whereas
in animals it follows a specific pattern. By analysing the osteons in the remains, it can be
determined if the remains are human. If the remains have been identified as human, then
further examination of the remains should be carried out.
One example to analyse the possible cause of death of the victim is through forensic
radiology. This involves the use of x-rays, tomography and MRI scans, these will analyse the
skeletal material, it can reveal the identity of the individual, the cause of death being
deliberate or accidental and if the cause would be fatal or if another factor lead to the death.
Scientists can discover configurations within the body that occur unnaturally by analysing the
images of the body. Some of these configurations include dislocations , fractures and
wounds. Additionally, the size of weapons can be determined through this type of imaging,
as well as the series of injuries the body encountered. Positive forensic radiology results
show patterns which discard normal injuries on the body. Often these everyday injuries can
be supported by health records so can be discarded from the investigation.
Another example is by determining the age of the individual by analysing the bone growth.
Analysts can determine the age group of the individual based on their development, by
looking at the bones. Biological profiling of a person's remains consists of their age, gender,
ancestry and stature. In order to determine the sex of remains, analysis of the skull and
pelvis are the most useful. A female pelvis is often wider than the male pelvis, to allow for
childbirth. Specifically in the female pelvis they have a larger pelvic inlet, they also have a
much larger pelvic arch and a shorter sacrum concavity.
Another identification process of the remains is by analysing the teeth to identify the
person's age. Analysing the teeth is very useful when identifying children, the stages at
which the teeth have erupted from the gums can indicate a child's age to the year. If the
individual is an adult, it can be determined what age they are, as to how worn down the teeth
are from chewing.
In children, their bones are much smaller and underdeveloped, the elderly have deteriorated
but fully developed bones, and adults have healthy, fully developed bones. Additionally, the
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