Unit 4B report: Examination of biological, chemical, and physical forensic evidence-
I am now training as a forensic scientist at the local forensic science laboratory in Ascertain Forensics in the
Malvern Hills Science Park. As a part of my training, I am required to analyse the biological, chemical, and physical
evidence collected from the crime at Canary Bridge (case number AE245). As a part of this report, I will be
discussing and evaluating a number of different analytical techniques to help in examining these three types of
evidence. As well as this, I will show the techniques I personally used for the evidence I had to analyse, and why I
decided to use these methods.
Analytical techniques for biological evidence:
Blood-
Kastle-Meyer test- (Presumptive)
This test is used as a presumptive test to determine whether a substance has traces of haemoglobin in it, which is
in blood. This is done using phenolphthalein and hydrogen peroxide, and when this is mixed with haemoglobin
(the molecule that carries oxygen in red blood cells), it reacts and produces a dark pink colour.
Method:
1. Firstly, spray a cotton swab with distilled water as well as the material you are testing, and swab it. Wet
the material as well if this is dry to make it easier to collect the sample.
2. Add a drop of ethanol onto the sample on the swab. Do this so as the haemoglobin is exposed so as the
test is more sensitive and has a bigger reaction.
3. Add a drop of phenolphthalein reagent onto the swabbed sample. This is done as when we add the
hydrogen peroxide a reaction will occur if haemoglobin is present.
4. After waiting for a few seconds, add a drop of hydrogen peroxide. So, if haemoglobin is present a reaction
should occur with the phenolphthalein reagent and the colour of the sample should change to a dark pink.
5. If it does become bright pink within the first 30 seconds of the reaction, that means that the sample tested
is a presumptive positive for blood. If it changes after 30 seconds, it is irrelevant to the test and does not
mean it is blood as the sample has most likely oxidised on their own with the air by this time.
Evaluation:
This is a very good test to use to find out if blood is present as it is a quick test, and it only takes up to 30 seconds
to develop. In addition, there are only a few steps to this, so it is easy to carry out and complete. Thanks to the
use of ethanol in the test, it is also very sensitive, so it can detect even the smallest bit of haemoglobin, down to
1:107. If you are to swab this for a Kastle-Meyer test, it does not damage it in any way, so more samples can be
done later if need be. This method is very cost effective, as there are only a few chemicals and equipment
necessary for it to be conducted. In addition, due to the small number of equipment, this test is easy to transport,
so the test can be conducted on the actual crime scene, if need be, so this is advantageous to the SOCOs, as it can
,make the testing less time-consuming, as if it isn’t blood, they wouldn’t have to waste as much time in the
laboratory analysing it.
However, there are some limitations to using this method of blood analysis, firstly being that there can sometimes
be false positives. If you have waited for over 30 seconds, the air can end up oxidising the sample instead, which
also turns the sample pink, so you need to ensure that the results are taken before 30 seconds. As well as this,
just because you get a positive test, doesn’t necessarily mean that it is blood. This test only looks for the presence
of haemoglobin, not specifically blood. If you do get a positive result for blood, this also doesn’t guarantee that it
is human blood, so other methods may need to be used to determine this. In addition, it only tells you whether it
is blood or not and doesn’t give you any more to go off on that, like who’s it could be. In terms of subjectivity,
there is a level of this in the Kastle-Meyer test. I believe this is due to looking at the results by eye, so if the swab
goes a bright pink, then it is positive, but some people may think something is bright pink when it’s actually not
and vice versa. Due to this, it decreases the validity of the results taken from this test, making it essential that a
confirmatory test is also conducted. While we can conduct this technique many times, due to us having to spray
the sample with water, it does dilute it, which means that eventually we wouldn’t have enough of the sample to
analyse sufficiently. Not only does this damage the evidence, but it also results in a decrease in yield of the
evidence each time the test is performed.
Control samples are necessary for this test as you cannot determine whether there are just traces of haemoglobin
in the material, or if it is blood. To do this, you should get a swab from the substance you are testing, as well as
another swab from an area on the material that does not contain the unknown substance, so then if that one is
negative, but the substance swab is positive, then you know that blood is likely present.
ABO blood type test-
The ABO test is used to find out what blood type the sample is, and this is determined by the type of antigens in
the blood, which are present on the surface of the red blood cells. Forensic scientists mix the blood sample with
antibodies against type A and B blood, and if the blood cells stick together, it shows what type of blood it is. This
can also be considered a confirmatory test due to it only resulting in agglutination if there is blood.
Method:
1. Put the samples of blood in in the right typing tray in all three wells. The suspect’s blood labelled “suspect
1”, and the knife sample labelled etc.
2. Add one drop of the anti-A serum into the wells that are labelled ‘A’ for each sample.
3. Add one drop of anti-B serum into the wells that are labelled ‘B’ for each sample.
4. Add one drop of anti-Rh serum into the wells that are labelled ‘Rh’ for each sample.
5. With a sterile toothpick, use a separate one for each sample and mix gently for 10-15 seconds.
6. Record the results, saying if there was agglutination or not.
7. Document what each of the blood types are.
Evaluation:
The ABO test is a very time efficient method as you can easily carry out multiple tests at the same time. As well as
this, it is also very easy to read the results of the test in comparison to other test methods like card testing. The
reaction also happens relatively fast when you are mixing the sample, so it is also time efficient in this aspect.
There is very little equipment required for this technique, making it very cost effective. In addition, this means
that it is easy to transport if need be due to the small amount that would need to be taken.
While this test is very useful in regard to the analysis of blood, there are some limitations of this to look out for. It
is possible for there to be a false positive or false negative result if there is any bacterial contamination on the
sample. Despite there being a set amount of blood types, everyone’s varies, so some may have less of a reaction
in comparison to others. In addition to this, different blood types in general may have greater reactions than
,others, like O and B may have a greater reaction than A or AB types. This test does have a level of subjectivity, as
the results are looked at by eye, so some people may believe that it is agglutinated, when it may not be, and vice
versa. To help this, two analysts should look at the results to ensure that they’re reliable. Due to having to use
droplets of the blood to do the test, we are going to have less and less the more tests we do, so we are limited by
how much blood sample we have. Due to this, we are damaging the evidence by using up the blood, as eventually
we will not have any more to test on. We placed the blood samples in separate vials, however, not all of this is
going be able to be taken out of the vial, which results the yield decreasing.
When doing this test, you should make sure to do controls first to ensure nothing is faulty. To do this, you would
test A cells with Anti-A, B cells with Anti-B, and B cells with Anti-A, and A cells with Anti-B. In addition, when
testing for Rh, you should test the Anti-D with a positive and negative control.
Crime scene analysis:
When it came to analysing the blood found at the crime scene, I had used the Kastle Meyer Test and the ABO
blood type test. We had decided to carry out the Kastle-Meyer test over any other as this is a reliable and time
efficient method of analysis. I believe that thanks to us having done a control in the beginning as well, this
increases the reliability and validity of our test results, as it ensures that there isn’t just haemoglobin present on
the items rather than in the blood. This test also seemed the most fitting to do as it is very sensitive to the
smallest of blood, so we knew we would get more accurate results, as well as the fact that we can swab the red
substance again if needed as we can conduct this test multiple times. The Kastle-Meyer test is only a presumptive
test though, so after this we chose to conduct the ABO blood typing test, due to it being confirmatory, as this can
determine if it is blood or not. We made sure to conduct a control before this technique, which increases the
validity of our results, and this is as we ensured that the antibodies were effective. To improve the reliability of
these test results, and to increase the reliability, next time I would like to conduct repeats, so ensure that the
results are consistent.
Hair-
Microscopy-
This is a test that requires the use of a microscope, so it is all done by eye. There are many characteristics that
need to be looked out for when analysing hair, as these all differentiate per person. This is seen in the inner
medulla, cortex, and the outer cuticle, and this structure is called morphology. The outer cuticle is made out of
overlapping scales, and it seen as transparent. The cortex is the largest part in the hair shaft, and this is where
most of the pigment is in the hair, called melanin, which changes per person. The inner medulla is a hollow tube
or a tube containing lots of cells, in the centre of the hair shaft.
Different medullas to look out for can be fragmented, when it is broken up unevenly, continuous, when it is
constant, interrupted, when it is broken up evenly, absent, where there is no medulla, and solid, when the
pigment covers both the medulla and the cortex. As well as this, if the cuticle is seen to be transparent, the hair is
natural, and if the cuticle isn’t, and the pigment is covering both the cortex and the cuticle, the hair has been
dyed. You can also tell whether it has been bleached by the yellow colour present due to the removal of all the
pigment granules. The length of the hair should also be documented, and this can simply be done using a ruler,
and the colour of the hair sample.
There are different characteristics to look out for depending on the type of hair it is, like where on the body it has
come from. For example, head hair is seen as circular or elliptical, hair from the eyebrows or eyelashes are also
circular, but also have narrowed ends. Beard hair is thick and a triangular shape, and this also contains a double
medulla. Body hair is oval or triangular in shape, and the ends are typically ragged and dull, and underarm hair is
the same, though this depends on if this hair is shaved or not. Pubic hair is also oval or triangular and can have a
buckling.
, Hair can be analysed to see many different things, for example, you can tell if the hair has been forcefully pulled
or has just fallen out judging by the roots of the hair. The root also contains cells with DNA that can be analysed.
You can also test for any drugs that may have been in the system, as well as if the person the hair belongs to has
any nutritional deficiencies.
Evaluation:
This is a useful method of analysis as we can easily collect samples from any suspects, as well as just simply having
to collect the hair from the crime scene, rather than it having to be more invasive. In addition, microscopy is very
low in cost, as there isn’t much equipment required. A light microscope is mainly used for the analysis of the hair,
meaning that the equipment can be easily transported if need be. Through the use of a microscope, we can
identify many details in the hair, so the analysis is very accurate and can easily be matched with another sample.
This method does not require damaging any of the evidence, as we only need to move it under a microscope, so
this can be done multiple times, and the results present themselves right away, as your observations are the
results rather than having to wait for a chemical reaction or anything. Every time the test is conducted, the
sample is not altered in any way, so there is no decrease in yield. Due to these facts, it makes the test very easy to
be conducted, as it is all done by eye, so as long as the analyst is confident in their knowledge, characteristics can
be easily identified. However, due to this all being done by eye, there is a risk of human error, so some mistakes
may be made which would lead to false and unreliable results, and this also gives the results a level of
subjectivity.
Crime scene analysis:
When analysing the evidence from the crime scene, I had used the method of microscopy to look at the suspects
hair samples as well as the sample collected from the crime scene. This had gone well as we managed to identify
all of the characteristics of each hair sample, and I believe that our results were all reliable. As well as this, we
managed to find one of the samples collected from a suspect that seemed to have matched the sample from the
crime scene. Next time to improve the reliability of the results we had collected, I would have liked to have
analysed multiple hair shafts from the sample suspect, as we have 25 strands in our sample. However, due to time
we only managed to analyse one of each sample. As well as this, we had used light microscopes, and I think it
would have been interesting to use different types of microscopes to possibly get a more detailed and accurate
reading on the characteristics of the hair. For example, I have researched about stereo microscopes, and though
they are more expensive to have, this would give us a better 3D image of the hair we are analysing, so we could
go into much more detail. As well as this, this type of microscope can also take photographs to we can look at it
longer later which would have been very useful to be. If the roots of the hair was available to us, I would have
liked to have analysed this as well, as you can get a DNA sample from this part of the hair. Next time, I would have
liked to have another set of eyes to double check and confirm my analysis, as this would increase the validity.
I am now training as a forensic scientist at the local forensic science laboratory in Ascertain Forensics in the
Malvern Hills Science Park. As a part of my training, I am required to analyse the biological, chemical, and physical
evidence collected from the crime at Canary Bridge (case number AE245). As a part of this report, I will be
discussing and evaluating a number of different analytical techniques to help in examining these three types of
evidence. As well as this, I will show the techniques I personally used for the evidence I had to analyse, and why I
decided to use these methods.
Analytical techniques for biological evidence:
Blood-
Kastle-Meyer test- (Presumptive)
This test is used as a presumptive test to determine whether a substance has traces of haemoglobin in it, which is
in blood. This is done using phenolphthalein and hydrogen peroxide, and when this is mixed with haemoglobin
(the molecule that carries oxygen in red blood cells), it reacts and produces a dark pink colour.
Method:
1. Firstly, spray a cotton swab with distilled water as well as the material you are testing, and swab it. Wet
the material as well if this is dry to make it easier to collect the sample.
2. Add a drop of ethanol onto the sample on the swab. Do this so as the haemoglobin is exposed so as the
test is more sensitive and has a bigger reaction.
3. Add a drop of phenolphthalein reagent onto the swabbed sample. This is done as when we add the
hydrogen peroxide a reaction will occur if haemoglobin is present.
4. After waiting for a few seconds, add a drop of hydrogen peroxide. So, if haemoglobin is present a reaction
should occur with the phenolphthalein reagent and the colour of the sample should change to a dark pink.
5. If it does become bright pink within the first 30 seconds of the reaction, that means that the sample tested
is a presumptive positive for blood. If it changes after 30 seconds, it is irrelevant to the test and does not
mean it is blood as the sample has most likely oxidised on their own with the air by this time.
Evaluation:
This is a very good test to use to find out if blood is present as it is a quick test, and it only takes up to 30 seconds
to develop. In addition, there are only a few steps to this, so it is easy to carry out and complete. Thanks to the
use of ethanol in the test, it is also very sensitive, so it can detect even the smallest bit of haemoglobin, down to
1:107. If you are to swab this for a Kastle-Meyer test, it does not damage it in any way, so more samples can be
done later if need be. This method is very cost effective, as there are only a few chemicals and equipment
necessary for it to be conducted. In addition, due to the small number of equipment, this test is easy to transport,
so the test can be conducted on the actual crime scene, if need be, so this is advantageous to the SOCOs, as it can
,make the testing less time-consuming, as if it isn’t blood, they wouldn’t have to waste as much time in the
laboratory analysing it.
However, there are some limitations to using this method of blood analysis, firstly being that there can sometimes
be false positives. If you have waited for over 30 seconds, the air can end up oxidising the sample instead, which
also turns the sample pink, so you need to ensure that the results are taken before 30 seconds. As well as this,
just because you get a positive test, doesn’t necessarily mean that it is blood. This test only looks for the presence
of haemoglobin, not specifically blood. If you do get a positive result for blood, this also doesn’t guarantee that it
is human blood, so other methods may need to be used to determine this. In addition, it only tells you whether it
is blood or not and doesn’t give you any more to go off on that, like who’s it could be. In terms of subjectivity,
there is a level of this in the Kastle-Meyer test. I believe this is due to looking at the results by eye, so if the swab
goes a bright pink, then it is positive, but some people may think something is bright pink when it’s actually not
and vice versa. Due to this, it decreases the validity of the results taken from this test, making it essential that a
confirmatory test is also conducted. While we can conduct this technique many times, due to us having to spray
the sample with water, it does dilute it, which means that eventually we wouldn’t have enough of the sample to
analyse sufficiently. Not only does this damage the evidence, but it also results in a decrease in yield of the
evidence each time the test is performed.
Control samples are necessary for this test as you cannot determine whether there are just traces of haemoglobin
in the material, or if it is blood. To do this, you should get a swab from the substance you are testing, as well as
another swab from an area on the material that does not contain the unknown substance, so then if that one is
negative, but the substance swab is positive, then you know that blood is likely present.
ABO blood type test-
The ABO test is used to find out what blood type the sample is, and this is determined by the type of antigens in
the blood, which are present on the surface of the red blood cells. Forensic scientists mix the blood sample with
antibodies against type A and B blood, and if the blood cells stick together, it shows what type of blood it is. This
can also be considered a confirmatory test due to it only resulting in agglutination if there is blood.
Method:
1. Put the samples of blood in in the right typing tray in all three wells. The suspect’s blood labelled “suspect
1”, and the knife sample labelled etc.
2. Add one drop of the anti-A serum into the wells that are labelled ‘A’ for each sample.
3. Add one drop of anti-B serum into the wells that are labelled ‘B’ for each sample.
4. Add one drop of anti-Rh serum into the wells that are labelled ‘Rh’ for each sample.
5. With a sterile toothpick, use a separate one for each sample and mix gently for 10-15 seconds.
6. Record the results, saying if there was agglutination or not.
7. Document what each of the blood types are.
Evaluation:
The ABO test is a very time efficient method as you can easily carry out multiple tests at the same time. As well as
this, it is also very easy to read the results of the test in comparison to other test methods like card testing. The
reaction also happens relatively fast when you are mixing the sample, so it is also time efficient in this aspect.
There is very little equipment required for this technique, making it very cost effective. In addition, this means
that it is easy to transport if need be due to the small amount that would need to be taken.
While this test is very useful in regard to the analysis of blood, there are some limitations of this to look out for. It
is possible for there to be a false positive or false negative result if there is any bacterial contamination on the
sample. Despite there being a set amount of blood types, everyone’s varies, so some may have less of a reaction
in comparison to others. In addition to this, different blood types in general may have greater reactions than
,others, like O and B may have a greater reaction than A or AB types. This test does have a level of subjectivity, as
the results are looked at by eye, so some people may believe that it is agglutinated, when it may not be, and vice
versa. To help this, two analysts should look at the results to ensure that they’re reliable. Due to having to use
droplets of the blood to do the test, we are going to have less and less the more tests we do, so we are limited by
how much blood sample we have. Due to this, we are damaging the evidence by using up the blood, as eventually
we will not have any more to test on. We placed the blood samples in separate vials, however, not all of this is
going be able to be taken out of the vial, which results the yield decreasing.
When doing this test, you should make sure to do controls first to ensure nothing is faulty. To do this, you would
test A cells with Anti-A, B cells with Anti-B, and B cells with Anti-A, and A cells with Anti-B. In addition, when
testing for Rh, you should test the Anti-D with a positive and negative control.
Crime scene analysis:
When it came to analysing the blood found at the crime scene, I had used the Kastle Meyer Test and the ABO
blood type test. We had decided to carry out the Kastle-Meyer test over any other as this is a reliable and time
efficient method of analysis. I believe that thanks to us having done a control in the beginning as well, this
increases the reliability and validity of our test results, as it ensures that there isn’t just haemoglobin present on
the items rather than in the blood. This test also seemed the most fitting to do as it is very sensitive to the
smallest of blood, so we knew we would get more accurate results, as well as the fact that we can swab the red
substance again if needed as we can conduct this test multiple times. The Kastle-Meyer test is only a presumptive
test though, so after this we chose to conduct the ABO blood typing test, due to it being confirmatory, as this can
determine if it is blood or not. We made sure to conduct a control before this technique, which increases the
validity of our results, and this is as we ensured that the antibodies were effective. To improve the reliability of
these test results, and to increase the reliability, next time I would like to conduct repeats, so ensure that the
results are consistent.
Hair-
Microscopy-
This is a test that requires the use of a microscope, so it is all done by eye. There are many characteristics that
need to be looked out for when analysing hair, as these all differentiate per person. This is seen in the inner
medulla, cortex, and the outer cuticle, and this structure is called morphology. The outer cuticle is made out of
overlapping scales, and it seen as transparent. The cortex is the largest part in the hair shaft, and this is where
most of the pigment is in the hair, called melanin, which changes per person. The inner medulla is a hollow tube
or a tube containing lots of cells, in the centre of the hair shaft.
Different medullas to look out for can be fragmented, when it is broken up unevenly, continuous, when it is
constant, interrupted, when it is broken up evenly, absent, where there is no medulla, and solid, when the
pigment covers both the medulla and the cortex. As well as this, if the cuticle is seen to be transparent, the hair is
natural, and if the cuticle isn’t, and the pigment is covering both the cortex and the cuticle, the hair has been
dyed. You can also tell whether it has been bleached by the yellow colour present due to the removal of all the
pigment granules. The length of the hair should also be documented, and this can simply be done using a ruler,
and the colour of the hair sample.
There are different characteristics to look out for depending on the type of hair it is, like where on the body it has
come from. For example, head hair is seen as circular or elliptical, hair from the eyebrows or eyelashes are also
circular, but also have narrowed ends. Beard hair is thick and a triangular shape, and this also contains a double
medulla. Body hair is oval or triangular in shape, and the ends are typically ragged and dull, and underarm hair is
the same, though this depends on if this hair is shaved or not. Pubic hair is also oval or triangular and can have a
buckling.
, Hair can be analysed to see many different things, for example, you can tell if the hair has been forcefully pulled
or has just fallen out judging by the roots of the hair. The root also contains cells with DNA that can be analysed.
You can also test for any drugs that may have been in the system, as well as if the person the hair belongs to has
any nutritional deficiencies.
Evaluation:
This is a useful method of analysis as we can easily collect samples from any suspects, as well as just simply having
to collect the hair from the crime scene, rather than it having to be more invasive. In addition, microscopy is very
low in cost, as there isn’t much equipment required. A light microscope is mainly used for the analysis of the hair,
meaning that the equipment can be easily transported if need be. Through the use of a microscope, we can
identify many details in the hair, so the analysis is very accurate and can easily be matched with another sample.
This method does not require damaging any of the evidence, as we only need to move it under a microscope, so
this can be done multiple times, and the results present themselves right away, as your observations are the
results rather than having to wait for a chemical reaction or anything. Every time the test is conducted, the
sample is not altered in any way, so there is no decrease in yield. Due to these facts, it makes the test very easy to
be conducted, as it is all done by eye, so as long as the analyst is confident in their knowledge, characteristics can
be easily identified. However, due to this all being done by eye, there is a risk of human error, so some mistakes
may be made which would lead to false and unreliable results, and this also gives the results a level of
subjectivity.
Crime scene analysis:
When analysing the evidence from the crime scene, I had used the method of microscopy to look at the suspects
hair samples as well as the sample collected from the crime scene. This had gone well as we managed to identify
all of the characteristics of each hair sample, and I believe that our results were all reliable. As well as this, we
managed to find one of the samples collected from a suspect that seemed to have matched the sample from the
crime scene. Next time to improve the reliability of the results we had collected, I would have liked to have
analysed multiple hair shafts from the sample suspect, as we have 25 strands in our sample. However, due to time
we only managed to analyse one of each sample. As well as this, we had used light microscopes, and I think it
would have been interesting to use different types of microscopes to possibly get a more detailed and accurate
reading on the characteristics of the hair. For example, I have researched about stereo microscopes, and though
they are more expensive to have, this would give us a better 3D image of the hair we are analysing, so we could
go into much more detail. As well as this, this type of microscope can also take photographs to we can look at it
longer later which would have been very useful to be. If the roots of the hair was available to us, I would have
liked to have analysed this as well, as you can get a DNA sample from this part of the hair. Next time, I would have
liked to have another set of eyes to double check and confirm my analysis, as this would increase the validity.
