Unit 23C assignment
Expert witness
Pass
Explain the forensic techniques used to analyse 2 types of biological evidence
Blood:
The most prevalent sort of bodily fluid discovered at crime scenes is blood. It's often linked to
serious acts like murder or sexual or violent assault. However, it may be found in more typical crime
scenes such as burglaries, muggings, and car thefts. Blood collected at a crime scene or on an item of
evidence is examined and analysed in forensic serology. A forensic scientist can employ a variety of
laboratory techniques, including:
- Presumptive colour tests can be used in forensics to identify if the sample is in fact blood,
more specifically human blood
- Blood typing methods can be utilised to identify what blood group it is
- Blood can also contain DNA which therefore can be analysed to give anymore information
for who the blood belongs to
Red blood cell antigens
Antigens, extracellular glycoprotein structures, are found within and protrude from the red blood
cell (RBC) membrane in both human and animal red blood cells. These antigens direct the cells to
express a certain blood-type profile, which determines a person's blood group. Different blood
group types are caused by differences in antigens on RBC membranes. Only a few distinct blood
group types exist, and the population can be categorized into groups of people who have the same
blood type. Although a person's blood group cannot be used to identify them, it may be used to rule
out people who have other blood group types. For instance, if a blood sample is retrieved from a
crime scene and laboratory examination determines the type is group AB, the sample can only be
traced to someone who has type AB, which is a wide group of people. If the suspect has blood type
O, however, they may be ruled out of the investigations because they cannot be the source of the
AB type blood.
Forensics blood typing analysis
Forensic blood typing analysis detects the blood type of a blood sample
recovered at a crime scene by determining which antigens are present on
the RBC surface. The serological method involves analysing antibodies and
antigens in the blood. As an immunological reaction to foreign antigens,
antibodies are produced in the blood. They attach to antigens and render
them inactive. In forensic procedures, A and B antigens and antibodies are
employed to determine the ABO blood group. Anti-A antibody serum is
tested on a little sample of blood. If the A antigen is present, the antibodies
bind to the antigen, causing the cells to clump together and produce a
visible, cloudy precipitate in the blood sample, this is known as
agglutination. Anti-B antibody is used to determine the presence or
absence of the B antigen, while anti-Rhesus antibody can also be used to
determine the presence or absence of the Rh D antigen.
,Fingerprints:
Fingerprints are the most prevalent sort of evidence discovered at crime scenes and are linked to a
variety of crimes. Individual fingerprints are biological traits that are unique to each person.
Fingerprints have significant evidential value because they may uniquely connect a person with a
crime scene or evidentiary object, which is the fundamental purpose of a criminal investigation.
Fingerprints are one of the last elements of the skin to decay, and in certain cases, they may be used
to identify deceased people months, if not years, after death.
Fingerprint analysts visually match the latent print from the crime scene to the fingerprint of a
suspect if the print is detailed enough. The general form of the prints, the shape and depth of the
ridges in the print, and the length of each ridge are all factors that analysts consider. According to
Henry’s system of classification there is 4 types of fingerprints patten these include:
- Loops
- Arches
- Whorls
Loops:
prints that recurve back on themselves, forming a loop Loops, which are divided into radial and
ulnar loops, make up around 60% of all pattern variations.
Arches:
Integrate simple arches and tented arches in a wave-like pattern. Tented arches are more
angular than regular arches. Arches account for around 5% of all pattern types.
Whorls:
Like miniature whirlpools, they produce circular or spiral patterns. Plain, central pocket loop
which is a loop with a whorl at the end of it, a double loop which looks like a S and an
accidental loop e.i irregular shaped. Which account for 35% of all patterns.
Fingerprint minutiae
To perform early comparisons and include or exclude a known fingerprint from
further examination, investigators employ the general pattern type (loop, whorl,
or arch). To match a fingerprint, the analyst compares minutiae, or ridge
features, of a suspect fingerprint to the same information in a known fingerprint.
An analyst comparing a crime scene print to a print on file, for example, someone
might gather prints with the same basic pattern type, then analyse the prints side
by side with a loupe to find precise details within the minutiae that matches. The
fingerprints are confirmed to be from the same individual if enough information
match, this is usually 16 matches.
Explain the forensic techniques used to analyse 2 types of chemical evidence
Gunshot residue:
There are a number of tests which can be carried out to detect the presence of gunshot residue at a
crime scene. These are colour change tests, and they are simple to perform, reliable, inexpensive,
and quick to perform so convenient for working on a crime scene. There are different tests used to
test for different parts of the residue. These include:
, Modified Griess Test
This detects the presence of nitrate residues expelled from the firearm's muzzle during firing. The
by-product of the combustion of smokeless gunpowder, the explosive within the firearm, is nitrate
residue. Any nitrite compounds that may be present on an item, such as victim clothes, will become
vivid orange as a result of nitrate residues being present during the Modified Griess Test.
The dermal nitrate test
Unburned gunpowder and nitrate traces on suspects' hands are detected using this method. The
hands are coated in hot paraffin wax, which is then removed when it has hardened. Any
gunpowder residue on the hands is transferred to the paraffin wax. Diphenylamine, a reagent that
turns blue in the presence of nitrates, is used to test the wax, and if it turns blue then the suspect
had gunpowder and thus the gun which could lead to a conviction.
The sodium rhodizonate test
This test identifies the presence of lead gunshot residues on a surface. The surface is sprayed with a
solution of sodium rhodizonate, which reacts with any lead on the surface and becomes bright pink.
When a solution of hydrochloric acid is added, it becomes blue, indicating the presence of lead.
Confirmatory tests for unknown white powder:
Presumptive testing and confirmatory tests are the two major kinds of analyses used to assess
whether an illegal drug is present in a sample. Presumptive tests are less accurate and show the
presence of an illegal substance. Confirmatory tests ensure that the chemical in issue is correctly
identified. Preliminary tests are done by the following things:
- Visual examination
The physical characteristics of the sample are examined with the naked eye or under a microscope in
the first step of analysis. Colour, shape, size, and marks can all reveal vital information about a drug's
identification.
- Instrumental analysis
Instrumental analysis is used in confirmatory testing to positively identify the contents of presented
sample. To achieve a definitive identification, a multi-step approach is usually required to separate
the different compounds, evaluate their chemical features, and compare them to reference sources.
This is known as qualitative analysis, and it establishes what drugs are present as well as whether
one or more of them are illegal.
Chemical presumptive tests can be used to detect the presence of particular chemical compounds in
drugs of abuse. These examinations have the virtue of being inexpensive. They are rapid, accurate,
and consistent, and the results are simple to determine because they are based on colour changes. A
little portion of the evidentiary drug sample is analysed using chemical reagents during the test. If a
chemical reaction happens with the drug being tested, these create distinct colours. Presumptive
drug tests are unreliable because they might yield false positive findings. They do, however, provide
information to forensic scientists that allows them to select the appropriate sort of confirmatory
analytical test.
There are a number of confirmatory tests that can be used to test for white powders, however the
most utilised in industry is mass spectrometry. Mass spectrometry is a very efficient analysis
technique for determining the structure and chemical characteristics of solid, liquid, and gas
