Unit 4 - Forensic Investigation Procedures in Practice
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Unit 4: Examination of Biological Evidence
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Unit 4 - Forensic Investigation Procedures in Practice
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A report that details how biological evidence is forensically tested through presumptive tests. Includes fingerprinting, bodily fluids, hair analysis and skeletal remains. Also includes images and suggestions for further analysis for each technique. Received the highest grade, P3, for this assignme...
Unit 4 - Forensic Investigation Procedures in Practice
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Examination of Biological Forensic Evidence
Introduction
What is biological evidence? Biological evidence refers to “samples of biological material—such as
hair, tissue, bones, teeth, blood, semen, or other bodily fluids—or to evidence items containing
biological material” (Ballou et al., 2013). Biological evidence is crucial in cases, not only to identify or
narrow a suspect list but to confirm the presence of biological matter that can later place a suspect
at a scene or on a victim. The four areas of biological evidence looked at in this report are
fingerprinting, hair analysis, bodily fluids, and skeletal remains.
Fingerprinting Techniques
Fingerprints are impressions left on a surface due to natural oils and sweat produced by the
fingertips. These impressions are in a unique pattern caused by ridges and furrows on the
individual’s skin. Fingerprints first begin to develop during prenatal development within the womb.
Lumps of stem cell tissue called ‘volar pads’ that grow under the skin, determine the main pattern of
the fingerprint; the ridges and furrows then appear around this formation. This form of evidence
only becomes biological once it has been lifted from a surface or object/s. Fingerprints can either be
patent or latent prints. Patent prints refer to those where the “material deposited from the finger is
visible to the unaided eye” (White, 2016), such as a finger covered in ink. Whereas latent prints refer
to those that cannot be seen unaided and therefore need
enhancing to be visually inspected/analysed.
Enhancement techniques facilitate the analysis and
recording of any identifying features such as ridge
endings; islands; deltas; crossovers; and bifurcations.
Additionally, fingerprints are one of the last features of a
body to decay making it an ideal way to identify an
individual if decomposition makes facial recognition
unviable. The quality of the print left is dependent on the
(Manickam, 2017)
surface, the pressure used, contact time, and the exterior
conditions; these can cause partial prints to be found. The techniques used to enhance prints include
powders, gentian violet, iodine fuming, superglue fuming, and ninhydrin fuming. All enhancements
should be photographed to be able to be presented to a jury or further digitally enhanced.
Powders
Powders are an exceptional way to get a clear and reliable print to then be visually
analysed. Powders come in varying colours and can even be magnetic to aid the
collection process. Selecting the correct coloured powder is critical and should be
decided on a case-to-case basis as not every colour will make the latent print the
most visible. For example, if there is a suspected latent print on a surface that is
black you would pick a white powder to make it observable rather than a black
powder. This technique works as when a small amount of the powder is dusted
over an area believed to be containing a latent print, the powder adheres itself to
the residue of oils and moisture left behind on the surface by the fingertips. Once the latent print is
visible it can be collected using j-lar tape and then analysed for identifying features. Powders are
most easily detected on smooth non-porous surfaces such as glass or plastics.
, Gentian violet
Gentian violet is no longer in widespread use due to its toxicity but was used in older cases and
should be understood to improve and reflect on its issues. This technique requires a sticky tape that
is non-water-soluble, a solution of gentian violet (a form of dye) mixed with
water, and the latent print that needs to be developed. When the latent
print is lifted onto the sticky side of the tape it is submerged in the gentian
violet solution then rinsed with distilled water. Staining occurs on the fatty
compounds and residue left by the fingers, leaving a clearly visible purple
coloured print. This technique, like using powders, works best on non-porous
surfaces.
(Marissa, 2011)
Iodine fuming
Iodine fuming is another chemical technique used to enhance latent prints. This technique, unlike
gentian violet or powders, works best on both porous and non-porous surfaces such as paper,
cardboard, or wood. To perform this technique the object suspected of
having the latent print on needs to be placed into a fuming cupboard with a
container containing a small amount of solid iodine. The fuming cupboard
causes sublimination of the iodine which produces concentrated vapors that
are absorbed by the unsaturated fats and oils left by the skin. The print
should appear as a dark yellow/brown colour. Due to the sensitivity of
iodine fuming it can often detect features on the latent prints that other
(MEL Science, 2015) techniques (such as powders) may not be able to do so as clearly
Ninhydrin
Much like iodine fuming, ninhydrin fuming is a chemical method of enhancement. Ninhydrin can
come in a pre-mixed aerosol can that is ready to be applied to the
suspected print. It can also come in crystal form which then needs to be
dissolved in a carrier such as acetone (easily done at room temperature).
This solution is applied evenly on the area of the suspected latent
print “(usually via a simple spray bottle)” (Powers Scientific, 2015).
Once applied the ninhydrin reacts with amino acids present from the
fingerprint residue. The reaction causes an intense purple dye that
reveals the fingerprint; the aforementioned colour is known as
‘Ruhemann’s purple’ after the man who discovered ninhydrin. For best results, this technique
(BVDA, 2014)
should be used on porous surfaces such as wood or paper.
Superglue fuming
Superglue or ethyl cyanoacrylate is used, once in vapor form, to
develop latent prints most effectively on non-porous surfaces. This
chemical method of developing prints can be done at a scene if
necessary (e.g. collecting prints from a doorknob). To perform this
technique the evidence needs to be placed into a developing chamber
(Jansen, 2019)
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