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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 &

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Presentation Transcript
slide1

BLOOD

SPATTER

ANALYSIS

CP Forensics

Alvarado

slide2

How A SOURCE OF

FORENSIC EVIDENCE?

1) Origin(s) of bloodstain2) Distance of bloodstain from

target3) Direction from which blood

impacted

slide3

4) Speed with which blood

left its source5) Position of victim &

assailant6) Movement of victim &

assailant7) Number of blows/shots

slide4

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

slide5

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.

slide6

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.

slide7

More rapid bleeding may

result in slightly larger

drops.

  • BUT, on the contrary,

slower bleeding does not

result in smaller drops.

slide8

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.

slide10

CATEGORIES OF

BLOOD STAINS

  • PASSIVE
  • TRANSFER
  • PROJECTED
slide11

PASSIVE

DEFINITION: drops created or formed by the force of gravity acting alone.

slide12

EXAMPLES:

Drops

Drip Patterns

Pools

Clots

slide14

TRANSFER

DEFINITION: created when a wet, bloody surface comes in contact with a secondary surface.

slide15

EXAMPLES:

Contact bleeding

Swipe or Smear

Wipe

Smudge

slide16

PICTURES:

A recognizable image of all or a portion of the original surface may be observed in the pattern.

slide17

PROJECTED

DEFINITION: created when an exposed blood source is subjected to an action or force, greater than the force of gravity.

slide18

EXAMPLES:

Arterial Spurt / Gush

Cast-Off

Impact Spatter

slide20

cATEGORIES OF

IMPACT SPATTER

Low Velocity

Medium Velocity

High Velocity

slide21

LOW VELOCITY

Relatively large stains4mm in size and greater.

Gravitational pull up to5 feet/sec.

slide22

MEDIUM VELOCITY

Preponderant stain size 1 to 4mm in size.

Force of 5 to 25 feet/sec.

slide23

HIGH VELOCITY

Preponderant stain size 1mm or greater.

Force of 100 feet/sec. or greater.

slide24

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.

slide25

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

slide26

Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.

70○ ANGLE

slide27

45○ ANGLE

10○ ANGLE

30○ ANGLE

5○ ANGLE

slide28

ANGLE

OF IMPACT

ANGLE of IMPACTis the acute angle formed between the direction of the blood drop and the plane of the surface it strikes.

slide30

By utilizing trigonometric functions, it’s possible to determine the impact angle for any given blood droplet.

slide31

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

slide32

EXAMPLE

Finding AOI

LENGTH = 5.9cm

WIDTH = 2.6cm

slide33

SOLUTION:

AOI = SIN-1 W / L

AOI = SIN-1 2.6/5.9

AOI = SIN-1 (.44)

AOI = 26.2°

slide34

POINT OF

CONVERGENCE

DEFINITION: The common point, on a 2 dimensional surface, over which the directionality of several bloodstains can be retraced.

slide35

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.

slide36

By drawing a line through the long axis of a group of bloodstains, the point of convergence can be determined.

LONG AXIS / LENGTH

slide38

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).

slide39

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.
slide40

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

slide41

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

slide42

Point of Origin

(3D --- use Z axis)