FRSC 1011H Chapter Notes - Chapter 10: Blood Residue, Satin, 100 Feet
2 May 2018
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Bloodstain Pattern Analysis
● Bloodstain pattern interpretation includes the following:
○ The direction from which blood originated
○ The angle at which a blood droplet struck a surface
○ The location or position of a victim at the time a bloody wound was
inflicted
○ The movement of a bleeding individual at the crime scene
○ The minimum number of blows that struck a bleeding victim
○ The approximate location of an individual delivering blows that produced a
bloodstain pattern.
● Surface texture is an importance in the interpretation of bloodstain patterns
● Rough surfaces, such as a concrete floor or wood, usually result in irregularly
shaped stains with serrated edges, possibly with satellite spatter.
● Satellite Spatter
○ Blood spatter around parent stain, with blood droplets whose pointed ends
face against the direction of travel.
● The pointed end of a bloodstain faces its direction of travel.
● It is possible to determine the impact angle of blood on a flat surface by
measuring the degree of circular distortion of the satin.
● A drop deposited at an angle of impact of about 90 degrees will be
approximately circular in shape with no tail or buildup of blood.
● Angle of impact
○ The angle of the source of the blood to the surface where it was
deposited. It can be estimated from the width to length ratio of the stain to
help determine the position of the victim or the weapon at the time when
the bleeding wound was inflicted.
● As the angle of impact deviates from 90 degrees, the satin becomes elongated in
shape.
● Buildup of blood will occur when the angles are larger, whereas longer and
longer tails will appear as the angle of impact becomes smaller.
● Quick Review
○ Individual bloodstains can convey to the bloodstain analyst the
directionality and angle of impact of the blood when it impacted a surface.
Bloodstain patterns may convey to the analyst the location of the victim
(who was bleeding) or suspect (who was causing the bleeding), the
movement of bleeding individuals, and the number of blows delivered.
○ Surface texture is of paramount importance in the interpretation of
bloodstain patterns; rounder drops generally are produced on smooth,
nonporous surfaces whereas rough surfaces result in irregular-edged
drops. However correlations between standards and unknowns are valid
only when identical surfaces are used.
○ The direction of travel of blood that stuck an object may be discerned by
the stain’s shape. The pointed end of a bloodstain always faces it direction
of travel.
● The most common type of bloodstain pattern found at a crime scene is impact
spatter.
● Impact Spatter
○ A bloodstain pattern produced when an object makes forceful contact with
a source of blood, projecting droplets of blood outward from the source.
● Different types of spatter
○ Impact spatter
○ Forward spatter
■ Blood that travels away from the source in the same direction as
the force that caused the spatter
○ Back spatter
■ Blood directed back toward the source of the force that caused the
spatter.
○ Low-velocity spatter
■ An impact spatter pattern created by a force traveling at 5 feet per
second or less and producing drops with diameters of greater than
4 millimeters
○ Medium-velocity spatter
■ An impact spatter pattern created by a force at 5 to 25 feet per
second and producing drops with diameters of between 1 and 4
millimeters (small drops)
○ High-velocity spatter
■ An impact spatter pattern created by a force traveling at 100 feet
per second or faster and producing droplets with diameters of less
than 1 millimeter (very fine droplets)
● Impact spatter patterns can offer investigators clues about the origin of the blood
spatter and therefore the position of the victim at the time of the impact.
● Area of convergence
○ The area on a two-dimensional plane where lines traced through the long
axis of several individual bloodstains meet. This approximates the
two-dimensional place which the bloodstains were projected.
● Area of origin
○ The location in three-dimensional space from which blood that produced a
bloodstain originated. The location of the area of convergence and the
angle of impact of each bloodstain is used to approximate this area.
● A common method for determining the area of origin at the crime scene is called
the “string method”
○ Find the area of convergence for the stain pattern
○ Place a pole or stand as an axis coming from the area of convergence.
○ Attach one end of a string next to each droplet. Place a protractor next to
each droplet and lift the string until it lines up with the determined angle of
impact of the drop. Keeping the string in line with the angle, attach the
other end of the string to the axis pole.
○ View the area of origin of the droplets where the strings appear to meet.
Secure the strings at this area.
● Quick Review
○ An impact spatter pattern occurs when an object impacts a source of
blood. This produces forward spatter projected forward from the source
and back spatter projected backward from the source.
Document Summary
The angle at which a blood droplet struck a surface. The location or position of a victim at the time a bloody wound was inflicted. The movement of a bleeding individual at the crime scene. The minimum number of blows that struck a bleeding victim. The approximate location of an individual delivering blows that produced a bloodstain pattern. Surface texture is an importance in the interpretation of bloodstain patterns. Rough surfaces, such as a concrete floor or wood, usually result in irregularly shaped stains with serrated edges, possibly with satellite spatter. Blood spatter around parent stain, with blood droplets whose pointed ends face against the direction of travel. The pointed end of a bloodstain faces its direction of travel. It is possible to determine the impact angle of blood on a flat surface by measuring the degree of circular distortion of the satin.
