BLOOD

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BLOOD SPATTER ANALYSIS
CP Forensics Alvarado
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How A SOURCE OF FORENSIC EVIDENCE?
1) Origin(s) of bloodstain2) Distance of
bloodstain from target3) Direction from
which blood impacted
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4) Speed with which blood left its source5)
Position of victim assailant6) Movement
of victim assailant7) Number of
blows/shots
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PROPERTIES OF BLOOD
BLOOD VOLUME

• On average, blood accounts for
• 8 of total body weight
• 5 to 6 liters of blood for males
• 4 to 5 liters of blood for females

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BLOOD VOLUME (con't)

• A 40 percent blood volume
• loss, internally or/and
• externally, is required to
• produce irreversible shock
• (death).
• A blood loss of 1.5 liters,
• internally or externally, is
• required to cause incapacitation.

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SURFACE TENSION

• Experiments with blood have shown that
• a drop of blood tends to form into a
• sphere in flight rather than the artistic
• teardrop shape.
• The formation of the sphere is a result of
• surface tension that binds the molecules
• together.
• This elastic like property of the surface
• of the liquid makes it tend to contract.

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• More rapid bleeding may
• result in slightly larger
• drops.
• BUT, on the contrary,
• slower bleeding does not
• result in smaller drops.

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• Blood cast from a moving
• source will tend to consist
• of smaller droplets.
• Blood behaves as a
• projectile in motion and
• obeys the laws of physics
• and mathematics.

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Fitting of an ellipse in blood drop
Tail or spine
Parent Drop
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CATEGORIES OF BLOOD STAINS

• PASSIVE
• TRANSFER
• PROJECTED

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PASSIVE
DEFINITION drops created or formed by the force
of gravity acting alone.
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EXAMPLES
Drops Drip Patterns Pools Clots
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PICTURES
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TRANSFER
DEFINITION created when a wet, bloody surface
comes in contact with a secondary surface.
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EXAMPLES
Contact bleeding Swipe or Smear Wipe Smudge
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PICTURES
A recognizable image of all or a portion of the
original surface may be observed in the pattern.
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PROJECTED
DEFINITION created when an exposed blood source
is subjected to an action or force, greater than
the force of gravity.
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EXAMPLES
Arterial Spurt / Gush Cast-Off Impact Spatter
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PICTURES
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cATEGORIES OF IMPACT SPATTER
Low Velocity Medium Velocity High Velocity
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LOW VELOCITY
Relatively large stains 4mm in size and greater.
Gravitational pull up to 5 feet/sec.
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MEDIUM VELOCITY
                                               
                    
Preponderant stain size 1 to 4mm in size. Force
of 5 to 25 feet/sec.
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HIGH VELOCITY
Preponderant stain size 1mm or greater. Force of
100 feet/sec. or greater.
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DIRECTIONALITY OF BLOOD
The spherical shape of blood in flight is
important for the calculation of the angle of
impact (AOI) of blood spatter when it hits a
surface.
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When a droplet of blood strikes a surface
perpendicular (90 degrees) the resulting
bloodstain will be circular. That being the
length and width of the stain will be equal.
90? ANGLE
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Blood that strikes a surface at an angle less
than 90 degrees will be elongated or have a tear
drop shape.
70? ANGLE
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45? ANGLE
10? ANGLE
30? ANGLE
5? ANGLE
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ANGLE OF IMPACT
ANGLE of IMPACT is the acute angle formed between
the direction of the blood drop and the plane of
the surface it strikes.
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(No Transcript)
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By utilizing trigonometric functions, its
possible to determine the impact angle for any
given blood droplet.
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By accurately measuring the length and width of a
bloodstain, the impact angle can be calculated
using the SIN formula below
AOI SIN-1 W / L
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EXAMPLE
Finding AOI
LENGTH 5.9cm WIDTH 2.6cm
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SOLUTION
AOI SIN-1 W / L AOI SIN-1 2.6/5.9 AOI SIN-1
(.44) AOI 26.2
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POINT OF CONVERGENCE
DEFINITION The common point, on a 2
dimensional surface, over which the
directionality of several bloodstains can be
retraced.
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Once the directionality of a group of stains
(one or two stains is not sufficient) has been
determined, it's possible to determine a 2D
point (or area) for the group of stains.
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By drawing a line through the long axis of a
group of bloodstains, the point of convergence
can be determined.
LONG AXIS / LENGTH
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Point of Convergence (2D)
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POINT OF ORIGIN
DEFINITION lies at a point in space above the
point of convergence. Measurement of the impact
angle allows for translation of the 2-D image
(convergence) into a 3-D one (origin).
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TO DETERMINE WHERE THAT POINT IS LOCATED

• First measure the distance
• from each blood stain
• along its central axis to the
• POC (distance y)
• 2) Then take the TAN of the
• degrees AOI.

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3) Third, multiply the TAN of the AOI by the
distance. 4) Measure that distance from the
floor up the perpendicular axis and you
will arrive at the Point of Origin
(PO) FORMULA PO TAN (AOI) x y
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EXAMPLE
Finding PO
GIVEN DISTANCE FROM BLOODSTAIN (to POC) 90cm
AOI (calculated from AOI formula) 30
SOLUTION PO TAN (30) x 90cm
PO .577 x 90cm 52cm
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Point of Origin (3D --- use Z axis)
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In practice (at a crime scene), strings, tapes
and protractors are commonly used.
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Computer programs can also be used.