Blood as Evidence

Blood Pattern Analysis The use of physics and math to

interpret bloodstain patterns within a forensic setting

May show:1. Activity at scene2. Number of blows3. Position of victim and assailant4. Whether death was immediate or delayed5. Weapon characteristics

History 1894 - Pitorowski wrote earliest reference to

bloodstain pattern analysis 1939 - Balthazard was first to use physical

interpretations of stains 1955 - Dr. Paul Kirkused bloodstain pattern

interpretation as a defense witness in the Sam Shepherd case

1971 - Professor Herbert MacDonnell promoted bloodstain pattern interpretation as a tool for modern criminalistics

1983 – The International Association of Bloodstain Pattern Analysis was formed

Blood collection Package in NON-air tight container,

such as a paper bag, so that no mold grows—dry blood can still be analyzed

 Properties of Human Blood

Circulates throughout body to transport oxygen, electrolytes, nourishment, hormones, vitamins, and antibodies to tissues an organs

Contains red blood cells (erythrocytes), white blood cells (leukocytes), plasma, and platelets

Held together by STRONG cohesive forces

Blood . . .

Does NOT fall in tear drop form (spherical) Will not break apart as it falls through air Is 6 times more viscous than water Has average volume of 0.05 ml (diameter = 4.56

mm)  Blood hitting surface

--hard smooth surface = creates little spatter --wood or concrete = create larger spatter

(fig. 11.2, pg. 192)

Spattered blood = random distribution of bloodstains

Significance of SPATTERED blood . . .

Allows for determination of area or location of origin of blood source(triangulation—see picture)

Place someone at a crime (on clothing) ***May determine mechanism that

created pattern (including speed of drop at impact, weapon used, direction of travel, angle of impact,)***

Look for Convergence!

Real Crime Scene

Get Computer Help(Software is available!)

Notice the “top view”!

Classify spatters (3): LVIS—low impact velocity impact

Force = up to 5ft/sec diameter= 4 mm+ Examples: blood drops into blood and footstep spatters

MVIS—medium velocity impact Force = 5-25 ft/sec diameter = 1-3 mm Examples: blood flicked off finger and blunt object used on victim

HVIS—high velocity impact Force = +100 ft Diameter = < 1mm Examples: gunshots and propellers

 Weapon used . . .

Impact spatters:1-Gunshot—mistlike pattern (<1mm blood spots)--Size range dependent on amount of blood, caliber of weapon, # of shots and location on body, hair/clothes --blowback or back spatter possible

2-Beating or stabbing—sizes 1-3 mm--depends on force and quantity of blood--only exposed blood makes spatter (not 1st blow)--type of weapon influences pattern

Size, Shape, and Directionality (deals with “flight” of bloodstain)

Direction of travel--Narrow end of elongated bloodstain points in direction of travel (impact angle < 90 degrees)--the tail will point in direction of travel

 --Circular bloodstain = no travel, dropped @ 90 degree angle

Impact Angle calculation (for elliptical bloodstains)

1st find ratio of width to length (see picture)

Then take the arc sin of that ratio

› Thus . . . Angle of impact = sin-1 (width/length)

Size, Shape, and Directionality (deals with “flight” of bloodstain)

sin θ = W / L

W

L

What does W = L mean?sin θ = 1 → θ = 90Drop is a circle!

Angle of Impact“The tail tells the tale”

90 degrees –

60 degrees –

30 degrees –

10 degrees –

Calculated point of origin Closer for high velocity spatter or when

stains originate closer to where the spatter occurred

Rule of Thumb: As impact angle goes down, bloodstain shape becomes more elongated.

Cast-off Bloodstains

Arterial Gushing

String Convergence in a 2 Dimensional Plane

Convergence

Other Patterns in Blood Transfer patterns (gun, knife, hand,

foot…) Void patterns (indicating some object

was removed or a person was hit by spatter)

Flow patterns (may indicate movement with change in flow)

Other Bloodstain patterns

Satellite or secondary spatter = single drops, circular or oval, 0.1=1 mm size

  Drip pattern = multiple, free falling drops

on horizontal surface  Castoff pattern = multiple blows to same

area where wound has occurred and blood has accumulated

Other Bloodstain patterns

Expirated patterns = blood that has pooled in lungs, sinuses, or airway passages is expelled from body

Arterial patterns = breaching of artery and result is gushing or spurts of blood

Blood transfer pattern = blood stained object contacts unstained object (can be a smear)

Dried blood = color changes . . . red –to— reddish brown —to— black

Clotting Time Clotting time outside the body ranges

from 3 – 15 minutes Spattered clots indicate that time

passed between the initial bleeding and later blows

Coughing of clotted blood may indicate post-injury survival of victim

Drying Time Drying begins at periphery and proceeds

inward Drying time is affected by

› Surface type› Amount of blood› Climatic conditions

Skeletonization› Partially dry stains leave a ring that outlines

original spatter› The drier the stain, the less skeletonization

shown

Documentation of Bloodstain

Document size, shape, and distribution of stains and patterns

Use photographs, video, diagrams, and notes

Collect articles of evidence with significant or questionable patterns

(Remember Luminol can be used to detect or enhance bloodstain patterns)