BLOOD SPATTER ANALYSIS. CP Forensics Alvarado. How A SOURCE OF FORENSIC EVIDENCE?. 1) Origin(s) of bloodstain 2) Distance of bloodstain from target 3) Direction from which blood impacted. 4) Speed with which blood left its source 5) Position of victim &
1) Origin(s) of bloodstain2) Distance of bloodstain from
target3) Direction from which blood
left its source5) Position of victim &
assailant6) Movement of victim &
assailant7) Number of blows/shots
8 % of total body weight
4 to 5 liters of blood for females
loss, internally or/and
externally, is required to
produce irreversible shock
internally or externally, is
required to cause incapacitation.
a drop of blood tends to form into a
sphere in flight rather than the artistic
surface tension that binds the molecules
of the liquid makes it tend to contract.
result in slightly larger
slower bleeding does not
result in smaller drops.
source will tend to consist
of smaller droplets.
projectile in motion and
obeys the laws of physics
Tail or spine
DEFINITION: drops created or formed by the force of gravity acting alone.
DEFINITION: created when a wet, bloody surface comes in contact with a secondary surface.
Swipe or Smear
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.
Arterial Spurt / Gush
Relatively large stains4mm in size and greater.
Gravitational pull up to5 feet/sec.
Preponderant stain size 1 to 4mm in size.
Force of 5 to 25 feet/sec.
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.
(90 degrees) the resulting bloodstain will be circular. That being the length and width of the stain will be equal.
Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.
ANGLE of IMPACTis 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
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
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).
the AOI by the distance.
4) Measure that distance from
the floor up the
perpendicular axis and you
will arrive at the Point of
FORMULA: PO = TAN (AOI) x y
DISTANCE FROM BLOODSTAIN (to POC): 90cm AOI (calculated from AOI formula): 30°
PO = TAN (30°) x 90cm
PO = .577 x 90cm
(3D --- use Z axis)
In practice (at a crime scene), strings, tapes and protractors are commonly used.