oct ewj 24 online - Flipbook - Page 81
indicate the location and movement of the individual
after the artery was severed.
Contact stains can include:
⁃ Transfer patterns such as a finger mark, footwear
mark or fabric mark in blood
⁃ Swipes where a bloodstained surface moves across
another surface
⁃ Wipes where wet blood already on a surface is wiped
across that surface
Airborne type patterns can include:
The Process of Blood Drying
The drying time of blood is influenced by numerous
factors, including temperature, humidity, airflow, and
the volume of the bloodstain.
Factors Affecting Drying Time:
1. Temperature: Higher temperatures accelerate the
drying process, while lower temperatures slow it
down. Blood on a hot, sunny surface can dry within
seconds, whereas in a cooler environment, it may take
much longer.
2. Humidity: High humidity levels can prolong drying
times, as the moisture in the air slows the evaporation
process. Conversely, low humidity speeds up drying.
3. Airflow: Increased airflow across a bloodstain
facilitates faster drying by promoting evaporation.
Stagnant air slows the process significantly.
Figure 1: This Image showing range of blood pattern types,
including cast off, drip stains etc.
4. Volume of Blood: Larger volumes of blood take
longer to dry than smaller volumes. A small blood
droplet on a non-porous surface might dry in a few minutes, while a larger pool can take hours or even days.
Drip Stains: Formed by blood falling under the
influence of gravity, drip stains can indicate the movement of a bleeding individual or item wet with blood.
The size and shape of these stains are influenced by
the volume of blood, the height from which it falls, and
the surface it contacts. Drip stains on non-porous surfaces like laminate flooring spread out forming larger
circular stains, while those on porous surfaces like
carpet appear smaller due to absorption.
5. Surface Type: The surface on which the blood lands
also affect drying times. Non-porous surfaces like glass
or metal allow blood to dry faster due to minimal
absorption, while porous surfaces like fabric or carpet
absorb blood, potentially extending the drying
process.
Impact Spatter: Created when an external force, such
as a blow, causes wet blood to break into droplets and
travel through the air forming spots on the
surrounding surfaces on which they land. The shape
and distribution of the resultant spots can help
identify where the source of the wet blood was when
struck and potentially a minimum number of blows
delivered on that wet blood.
Practical Implications:
Accurately estimating the drying time of blood
remains challenging due to the multitude of influencing factors. Environmental conditions at the crime
scene, such as fluctuating temperatures or varying humidity levels, can complicate assessments. Additionally, bloodstains on different materials or in various
locations within the same scene might dry at different
rates. Therefore, it is generally not possible to give
anything more than approximate time frames at best.
Cast-Off Patterns: These occur when blood is flung
from a blood-bearing object in motion, such as a
weapon or hand. Cast-off patterns typically form a linear pattern of stains, that can assist in addressing
where the item was when it moved.
The Role of DNA in Blood Pattern Analysis
DNA analysis is a critical component of forensic
investigations, particularly in conjunction with BPA.
Identifying the potential source of bloodstains
through DNA profiling allows forensic scientists to link
blood evidence to specific individuals, thereby
strengthening the reconstruction of crime scenes.
Gunshot Spatter: This typically appears as a fine mist
of blood droplets. This type of spatter can help identify the positions of the shooter and the victim. Gunshot spatter can include forward spatter, produced as
the projectile exits the body, and back spatter, directed
back towards the shooter as the projectile enters.
DNA Profiling of Bloodstains:
Once blood is detected and its patterns are analysed,
DNA profiling can be performed to determine the
blood's potential origin. Forensic scientists can extract
DNA from even minute quantities of blood, obtaining a profile that can be compared to known
reference samples.
Expirated Blood: Blood expelled from the mouth,
nose, or a wound to the lungs/airways, often mixed
with saliva, creating a pattern that can be mistaken for
impact spatter. Characteristics like air bubbles within
the stains can help differentiate expirated blood from
impact spatter, however in some instances it will not
be possible to determine whether the pattern is the
result of impact or expiration.
Human vs. Animal Blood:
Chemical tests like KM and luminol do not distinguish
between human and animal blood. However, the
DNA profiling techniques used are specific to areas of
human DNA and so if a DNA profile is obtained, this
indicates the blood is human in origin. Therefore,
DNA analysis is essential to confirm the human origin
of bloodstains.
Arterial Patterns: When an artery is breached, blood
is pumped out under high pressure, creating distinctive patterns known as arterial gushes and spurts.
These patterns are produced with each heartbeat,
forming characteristic clusters of stains that can
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