Download Blood splatter analysis

Student Name: _____Maria Alice Ciobanu______________________
Student ID:_____ 3395606__________________________
Blood evidence
Part 1: Physiology of Blood (30%of Mark)
Q) Name and describe in detail the three main formed elements in blood
The red blood cells (erythrocytes) account for 99% of formed elements. In most mammals
mature erythrocytes are biconcave discs that have no nuclei. The cell consists mostly of
haemoglobin and stroma. The amount of the erythrocytes contained by adult human blood
is 4.5-5.8 x 1011 per decilitre. Due to their ability to deform shape, they can pass through
capillaries in the peripheral circulation, although they have approximately 8 µm in diameter.
Erythrocyte formation (erythropoiesis) takes place in the bone marrow in the adult, and in
the liver, spleen and bone marrow of the fetus. After 120 days in the circulation they are
removed by the reticulo-endothelial system of the spleen and liver. The main functions are
the transport of oxygen from the lungs to the tissue, the maintenance of blood pH and to
facilitate the buffering capacity of blood (Russell et al 1982).
The leucocytes (white blood cells) represent about 1%volume of formed elements. Blood
contains approximately 7.5 x 108 white cells per decilitre, their size varying between 1020µm in diameter. Five types of leucocytes are classified by the presence or absence of
granules in the cytoplasm of the cell; the agranulocytes (lymphocytes and monocytes) and
the granulocytes (neutrophils, basophils and eosinophils). Their overall lifespan is probably
a few days and they are concerned with the immune response of the body, acting as
phagocytes, detoxifiers and immune system cells. The defence of the body is realized by
the B lymphocytes which produce antibodies and T lymphocytes which participate in various
cellular immune reactions (Russell et al 1982).
Comprising 0.5 per cent of the blood volume, platelets are small blood cells which are
synthesized in the bone marrow from megakaryocytes. Thrombocytes are not nucleated,
but they contain large numbers of membrane-enclosed granules and dense bodies with a
high affinity for collagen and elastin fibres and adhere to them at the site of vessel-wall
damage in order to prevent blood-loss. These disc shaped blood cells have a diameter of 2
to 4 µm playing a crucial role into clotting mechanism of blood (Russell et al 1982).
Part Two: Blood testing (30% of Mark)
Q) Describe in detail a test that can be used for the detection of trace blood?
The base of the presumptive tests is represented by the ability of the haemoglobin existent
in erythrocytes to catalyse the oxidation of certain reagents. The most commonly used
reagent is phenolphthalein, which in its reduced form is colourless but purple/fuchsia
coloured in the oxidised state. Colour-change tests are able to identify minute amounts of
blood, for example in cracks in the walls and floors. Forensic analysts use the Kastle Mayer
test usually for determining if the composition of a stain contains blood before carrying out
other more complicated blood-specific test. However, this presumptive test has its
disadvantages due to the fact that phenolphthalein cannot distinguish between human
blood, other animal blood or vegetable peroxidases (James and Nordby, 2005).
Q) Describe in detail the precipitin test for blood
The precipitin test is based on an antibody-antigen complex, in order for the origin of a
bloodstain to be determined whether it is human or animal. This test utilizes simple diffusion
between an antiserum and an extract from the bloodstain in a test tube. If the blood is
human, dissolved antigens and antibodies from the antiserum layer will start to diffuse into
the other layer, resulting into a fine line of precipitate on the interface of the two solutions.
No reaction will be visible if the extract is animal (James and Nordby, 2005).
Q) Describe the theoretical principles of the ABO blood typing system.
In order for a human origin bloodstain to be associated with a particular individual, ABO
blood typing system represents a serological technique of a great ability in the field of
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Student Name: _____Maria Alice Ciobanu______________________
Student ID:_____ 3395606__________________________
forensic analysis. This human antigenic system is based on the existence or the absence of
antigens on the surface of the erythrocytes and corresponding antibody within the blood
plasma. Therefore, an agglutination reaction which will bind the red cells together will occur
if an individual receives the incorrect blood group. Forensic testing for the presence of
antibodies commonly uses the absorption-elution for antigenic characteristics and the Lattes
Crust test (White, 2005).
Part 3: The effect of angle on blood splatter shape (40% of Mark)
Calculations: Using the equation provided below, calculate the angle of the six blood drops.
Width: 4mm
Blood drop one
Blood drop two
Length: 6mm
Width: 3mm
Blood drop four
Angle 41.81
Angle 14.47
Width: 9mm
Width: 7mm
Length: 9mm
Blood drop five
Angle 90
Width: 2mm
Blood drop three:
Length: 12mm
Length: 7mm
Length: 9mm
Angle 51.05
Width: 5mm
Blood drop six
Length: 25mm
Angle 16.60
Angle 11.53
Q) Describe in detail the principles of ‘Cast-off’ blood pattern analysis
Cast-off patterns represent the effect produced by blood when it is released or thrown from
a secondary moving object that is soaked with blood. In order for a cast-off bloodstain
pattern to be formed, the centrifugal force generated by a swinging bloodied object needs to
be sufficiently great to overcome the adhesive force that holds the blood to the weapon. An
important characteristic of this pattern is the linear distribution of individual drops of blood,
which may appear curved or straight depending on the circumstances of its deposition. Also
it can be ascertain the direction in which droplets of blood were travelling when they hit
adjacent surfaces and the relative positions of the victim and suspect. Furthermore,
information about the type of the instrument used in the attack and the number of blows
struck can be revealed when carefully examining cast-off bloodstains. (James and Nordby,
2005)
Q) Describe in detail the effect of force on the formation of blood splatter
When sufficient force is available to overcome the surface tension of blood, spatter is
created. The resulting bloodstains vary considerably with gunshot, stabbing or beating
events. Therefore, if the force applied has a low velocity impact\force (1.5m\s), the diameter
of blood droplets are typically greater than 3 mm, depending also on the availability of the
exposed blood. Impact spatter associated with stabbing and blunt force (medium velocity
impact\force) is around 1.5-7m\s and generally exhibits a size range from 1 to 3 mm in
diameter. When the misting effect is observed or satellite spatter is produced by blood, they
usually are associated with gunshot, explosions and high-speed machinery impact. If
associated with an entrance wound, back spatter can be observed. The force applied in this
case can reach 30m\s or more, exhibiting a wide size range from less than 1 mm in
diameter. (Pepper, 2005)
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Student Name: _____Maria Alice Ciobanu______________________
Student ID:_____ 3395606__________________________
References:
1. Jackson, A.R.W. and Jackson, J.M. (2004) Forensic Science. Harlow:
Pearson.
2. James, S.H. and Nordby, J.J. (2006) Forensic Science: An Introduction
to Scientific and Investigative Techniques (2nd Ed.). Prentice Hall
3. Russell, N.J. Powell, G.M. Jones, J.G. Winterburn, P.J. and Basford J.M.
(1982) Blood Biochemistry. Billing &Sons, Worcester.
4. Pepper, I.K. (2005) Crime Scene Investigation., Milton Keynes. Open
University Press.
5. Sutton, R. & Trueman, K. (2009) Crime Scene Management – Scene
Specific Methods. Wiley.
6. White, P. (ed) (1998) Crime Scene to Court: the essentials of forensic
science. London. Royal Society of Chemistry.
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