blood as evidence
DESCRIPTION
Blood as Evidence. Blood Pattern Analysis. The use of physics and math to interpret bloodstain patterns within a forensic setting May show: Activity at scene Number of blows Position of victim and assailant Whether death was immediate or delayed Weapon characteristics. History. - PowerPoint PPT PresentationTRANSCRIPT
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)