Unit 4 - Forensic Investigation Procedures in Practice
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Unit 4: Assignment 1 - Examination of biological forensic evidence
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Unit 4 - Forensic Investigation Procedures in Practice
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PEARSON (PEARSON)
A report detailing three forms of biological evidence and how they are analysed in a forensic investigation. Minor discussion on further techniques is included, though not a requirement, as the criteria for this report is capped at pass level.
Unit 4 - Forensic Investigation Procedures in Practice
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Examination of biological forensic evidence
Luke David Farrar
Introduction
This report will describe the analytical techniques that forensic scientists use to
examine types of biological evidence. This includes bodily fluids, fingerprints, hair, and
skeletal remains.
Bodily fluids
Some of the most useful bodily fluids to collect for evidence are blood, saliva, and
semen. By definition, bodily fluids are biological evidence, making them invaluable in an
investigation as they can provide DNA profiles of both the suspect and victim.
Blood analysis: Kastle-Meyer
A common presumptive test used in blood analysis is
Kastle-Meyer. Here, the sample presumed to be blood is
swabbed; then, a drop of phenolphthalein reagent, a colourless
indication solution, is applied to the swab, and. Then, a drop of
hydrogen peroxide is also applied to the swab.
In the presence of haemoglobin, these compounds oxidise
and rapidly produce a clear, pink stain. A rapid colour change is
needed to have confidence in the tests result since
Results from a Kastle-Meyer test are not conclusive but
can indicate the need for further analysis of evidence.
Blood analysis: Leucomalachite green The results of my Kastle-
A moderately toxic presumptive rest that produces a Meyer test, showing a
distinct green colour when catalysed with haemoglobin and positive for the presence of
hydrogen peroxide. Due to the similar nature of this test to that of haemoglobin.
the Kastle-Meyer test, the latter is preferred as it is less toxic to
humans.
Much like the Kastle-Meyer test, a swab is used on our presumed blood sample—we
can use sterilised water to moisten the swab if necessary. Then, we apply 1-2 drops of our
LMG reagent and observe for a green colour change. If there is no colour change, we repeat
the process using 1-2 drops of 3% hydrogen peroxide.
Blood analysis: Luminol
A chemiluminescent crystalline solid that produces light when reacting with the iron
in haemoglobin. This test often produces false positives—reacting to chemical compounds,
such as cleaning detergent—but is quick to do and narrows down the areas of a crime scene
which need further investigation. It can also be sprayed, allowing coverage of a large area to
be completed faster than swabbing each individual location and conducting a Kastle-Meyer
or Leucomalachite green test.
, Seminal analysis: Acid Phosphatase Test
Strips containing starch detect the presence of acid
phosphatase—an enzyme secreted by the prostate gland—in our
sample. If our paper turns black/blue, we have a positive reaction for
the presence of acid phosphatase in our sample. However, since this is
a presumptive test, further analysis is needed to be confident in our
results/be used in the court of law.
Saliva analysis: Starch test
A presumptive test where pre-coated
sheets with starch microspheres are used to detect A swab containing a
the presence of amylase—a digestive enzyme light-yellowish sample,
abundant in saliva—by determining whether the suspected to be
collected sample digests the starch on our sheets. semen, from an article
The test is as simple as swabbing our of clothing.
sample and transferring it onto our pre-coated sheets, making it both
quick and affordable to carry out.
Fingerprints
A positive reaction
Latent fingerprints can be cross-referenced against those in a
to the presence of
global database to determine who the prints belonged to, due to the
amylase in my
distinctive features unique on an individual basis. The most common
suspect sample.
prints obtained from crime scenes are partial prints. Fortunately, these
prints are still identifiable, even if only half of the print is physically obtained.
Fingerprints can be considered both physical and biological evidence, depending on
the location the print is taken from. If the print is directly from someone’s finger it is
considered biological. Whereas, if the print is taken from a surface, it is considered physical
evidence, as we are analysing the remnants of dirt, grease, oils and sweat; relative to the
pressure, time and point of contact the finger left on the surface.
Gentian violet
A specialised technique used to develop latent prints
using an adhesive—such as insoluble tape. The gentian violet
itself is a chemical substance that dyes the oil in the prints a
violet colour to enhance them.
Powders
Multiple different types of powders are used, depending
on the surface, to collect prints from a crime scene. They are
quick and easy to do as they only require an adhesive (JLAR
tape) and the powder itself in order to enhance a print.
Black and white: Great contrast for the print when against
dark/light surfaces. Useful for photography for the same reason. Gentian violet being used to
Mostly used on non-porous surfaces, such as kitchen or bathroom enhance a print, though the
tiles, metallic surfaces, dishes and possibly door handles, print is still difficult to
depending on the colour. discern.
Fluorescent: Stands out the most on multi-coloured surfaces. Would
be more useful than black and white powders on, for example, a children’s toy, a marbled
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