1) origin(s) of bloodstain 2) distance of bloodstain from target 3) direction from which blood...
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1) Origin(s) of bloodstain2) Distance of bloodstain from target3) Direction from which blood impacted
4) Speed with which blood left its source5) Position of victim & assailant6) Movement of victim & assailant7) Number of blows/shots
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
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.
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.
More rapid bleeding may result in slightly larger drops.
BUT, on the contrary, slower bleeding does not result in smaller drops.
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.
“Fitting” of an ellipse in blood drop
Tail or spine
Parent Drop
• PASSIVE• TRANSFER• PROJECTED
DEFINITION: drops created or formed by the force of gravity acting alone.
EXAMPLES:
DropsDrip Patterns
PoolsClots
PICTURES:
DEFINITION: created when a wet, bloody surface comes in contact with a secondary surface.
EXAMPLES:
Contact bleeding Swipe or Smear
Wipe Smudge
PICTURES:
A recognizable image of all or a portion of the original surface may be observed in the pattern.
DEFINITION: created when an exposed blood source is subjected to an action or force, greater than the force of gravity.
EXAMPLES:
Arterial Spurt / GushCast-Off
Impact Spatter
PICTURES:
Low Velocity
Medium Velocity
High Velocity
LOW VELOCITY
Relatively large stains 4mm in size and greater.
Gravitational pull up to 5 feet/sec.
MEDIUM VELOCITY
Preponderant stain size 1 to 4mm in size.Force of 5 to 25 feet/sec.
HIGH VELOCITY
Preponderant stain size 1mm or greater. Force of 100 feet/sec. or greater.
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.
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
Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.
70○ ANGLE
45○ ANGLE
30○ ANGLE
10○ ANGLE
5○ ANGLE
ANGLE of IMPACT is the acute angle formed between
the direction of the blood drop and the plane of the
surface it strikes.
By utilizing trigonometric functions,
it’s possible to determine the impact angle for any given
blood droplet.
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
LENGTH = 5.9cm
WIDTH = 2.6cm
Finding AOI
SOLUTION:
AOI = SIN-1 W / L
AOI = SIN-1 2.6/5.9
AOI = SIN-1 (.44)
AOI = 26.2°
DEFINITION: The common point, on a 2 dimensional surface, over which the directionality of several bloodstains can be retraced.
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.
By drawing a line through the long axis of a group of bloodstains, the point of
convergence can be determined.
LONG AXIS / LENGTH
Point of Convergence (2D)
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).
1) 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.
TO DETERMINE WHERE THAT POINT IS LOCATED:
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
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
Point of Origin(3D --- use Z axis)
In practice (at a crime scene), strings, tapes
and protractors are commonly
used.
Computer programs can also be used.