Unit 23 - Forensic Evidence, Collection and Analysis
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DISTINCTION - BTEC Applied Science Unit 23 LA C&D: Expert Witness.
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Unit 23 - Forensic Evidence, Collection and Analysis
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PEARSON (PEARSON)
Distinction level: BTEC Applied Science Unit 23 LA C&D.
C: Conduct scientific analysis of physical, biological and chemical evidence.
D:Be able to justify methods, interpret findings and report on conclusions of forensic techniques and analysis.
Unit 23 - Forensic Evidence, Collection and Analysis
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Unit 23 LAC&D Expert Witness name
SOME DATA WERE REMOVED DUE TO PRIVACY
Forensic Report:
I work for the British Transport Police's Scientific Support Unit as a trainee forensic
technician. As a trainee, I'm also expected to act as an 'expert witness,' analysing material
supplied to me from the crime scene, developing conclusions, and reporting on my findings.
In front of a 'mock court,' I will submit my findings on the evidence.
Biological:
Blood test:
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. Blood, on the other hand, may be found
at more common crime scenes. 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:
● To acquire a preliminary indication if the sample is blood, presumptive colour tests
might be utilised.
● The blood type can then be determined using blood typing procedures.
● Blood may contain DNA evidence that may be analysed to determine the blood
source's identity.
Presumptive blood tests:
The haemoglobin (Hb) found inside red blood cells reacts to presumptive blood tests.
Mammalian and other animal red blood cells contain haemoglobin, an iron-containing
protein. Its function is to carry oxygen from the lungs to the rest of the body. The tests are
based on the haemoglobin's capacity to catalyse reagent oxidation.
Kastle-Meyer presumptive blood test:
The Kastle-Meyer technique is a presumptive technique used to detect whether or not blood
was present at a crime scene. The iron in haemoglobin is used in the Kastle-Meyer test.
When phenolphthalein is combined with hydrogen peroxide and blood, it becomes pink and
oxidises to phenolphthalein and water. The hydrogen peroxide in the blood combines with
the haem component of haemoglobin, which works as a peroxidase, converting the peroxide
to water.
Equipment list for presumptive blood testing (Kastle-Meyer):
● Water
● Cotton swab
● Hydrogen peroxide
● Ethanol
● Kastle-Meyer reagent - phenolphthalein indicator.
● Blood sample
Method for presumptive blood testing (Kastle-Meyer):
1. If the blood is dry, add a few drops of water to the cotton swab to dampen it.
2. Swab the blood sample with the damp cotton swab.
3. Add drops of ethanol followed by a few drops of the Kastle-Meyer reagent
(phenolphthalein indicator) and hydrogen peroxide.
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4. If the result is positive, the swab will turn pink immediately.
Part C.P5
Conclusion, results, analysis and evaluation:
This test was used because it gives positive results immediately and is very sensitive, which
increases the reliability of the results. One limitation of this test is that other similar
substances can give false positive results and that is expensive (costing about £40-£80).
Because the tests are pricey, and if many testing were done, the overall cost would be
greater. This is a limitation since testing blood using a less expensive process may be more
cost efficient. The cotton swab turned pink immediately, which means that there was a trace
of blood in the cotton pad. This test is indestructible, so it can be used for further analysis,
like DNA fingerprinting. This method was easy to carry out because there was no
quantitative data to analyse and it was easy to spot the colour change. As the results were
positive, it increases the probability of someone else being with the victim at the crime
scene. It was easy to analyse this method as all we had to do was see if there was a colour
change from white to pink (qualitative data).
Part D.P7, C.M4, CD. D3
Other Chemical presumptive tests:
Presumptive tests are colour-changing chemical reagent tests that can identify the presence
of body fluids (saliva, blood and semen). They are sensitive, rapid, easy, and inexpensive
procedures that may be performed both on the scene and in the lab.
Presumptive tests for body fluids
Before collecting any fluid or stain that may be a bodily fluid, a presumptive test should be
performed at the crime scene. Chemicals are applied to the stains, and a change in colour
indicates the presence of bodily fluid.
Leucomalachite Green (LMG) presumptive blood test
The LMG test is a presumptive blood test that is non-toxic, highly specific, and has a low
sensitivity. It produces a lot of false positives and can detect 1 ml of blood in 10,000 ml of
water. In the presence of blood, the LMG reagent, also known as McPhail's reagent,
changes colour from colourless to dark blue-green, indicating the presence of haemoglobin
peroxidase enzyme activity. Because the LMG reagent is DNA-destructive, it should not be
used directly on a suspected blood stain.
Luminol
When combined with an oxidising agent, Luminol (CH2N3O2) produces blue
chemiluminescent light. When blood stains are detected but not visible to the naked eye, a
broad area can be sprayed with luminol reagent and studied in the dark.
Part CD.D3
ABO typing:
Based on the presence or lack of antigen 'A' and antigen 'B' on the surface of RBCs, Karl
Landsteiner classified human blood into four groups: A, B, AB, and O.
● Blood type A is defined as a person who has exclusively A antigens on the surface of
their RBCs.
● Type B people are those who solely carry B antigens on their skin.
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● The blood type AB is formed when both A and B are present.
● The blood type is group O if neither of the antigens are present.
Individuals can have any mix of blood antigens since they are inherited separately. 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.
● When anti-A antibody serum is introduced to a blood sample, a precipitate forms, but
no precipitation forms when anti-B antibody serum is added, the blood sample is
blood group A.
● When anti-B antibody serum is added to a blood sample, a precipitate forms, but no
precipitation forms when anti-A antibody serum is added, the blood sample has blood
group B.
● When anti-A and anti-B antibody serum are added to a blood sample, a precipitate
forms, indicating that the blood sample is blood type AB.
● When anti-A and anti-B antibody serum are added to a blood sample, no precipitate
forms, indicating that the blood sample is blood group O.
● When anti-D antibody serum is added to a blood sample, a precipitate forms,
indicating that the blood sample is Rh+.
● When anti-D antibody serum is added to a blood sample and no precipitate forms,
the blood group is Rh-.
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