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Blood
Blood
Is it Blood?
- Obvious
- Not always an easy determination
- Not Obvious• Not Obvious
- Stains on clothes, carpet, etc.
- Presumptive Tests – Blood indicated on…
- Confirmatory Tests – Blood identified on…
- Stains not visible (attempted cleaning)
- Luminol – A type of presumptive test
Is it Human Blood?
- Species determination
- Different species = different proteins
- Precipitin Test
- Antibody, antigen test
- If human, then the blood will precipitate its protein
Blood Evidence
- Blood found at a crime scene can be analyzed
(utilized as evidence) in a variety of ways:
- Genetics (molecular make-up for individualization)
- Toxicology (foreign substances i.e. toxins)
- Bloodstain Patterns (how blood was distributed)
Blood Spatters
- NOT Blood Sp L atters – no “L”
- Crime scene reconstruction
- Validity of statements made by witness, victim, and suspect
- International Association of Bloodstain Pattern Analysts (IABPA) - Organization of forensic experts specializing in the field of bloodstain pattern analysis - Promotes education / research and establishes training standards in the field of bloodstain pattern analysis
Author: Herbert Leon MacDonell current IABPA Historian
Laboratory of Forensic Science, P.O. Box 1111 Corning, NY 1483014830
Blood Spatters
May Reveal:
- Origin(s) of bloodstain
- Distance of bloodstain from target
- DiDi rection from which blood impactedti f hi h bl d i t d
- Speed with which blood left its source
- Position of victim & assailant
- Movement of victim & assailant
- Number of blows, shots, etc.
Liquid Blood
- Physical properties
- Viscosity
- Surface tension
- Both are about the same as water
- Behaves as a projectile in motion
- Gravity as only force – falls vertically
- Gravity with another force – falls vertically and horizontally at the same time
Surface Tension
- Resistant to penetration & separation
- Acts to reduce surface area
- A sphere offers the smallest surface area to volume ratio so free falling blood drops are spherical (not “teardrop”) on impact
Dripping Blood
Blood drop grows until Wt (G) > S.T. Single drop breaks free (teardrop shape) Surface tension pulls in vertically
Gravity is the only force acting
Surface tension pulls in vertically
Shape settles into sphere (0.05 ml)
Does not break up until impact
And horizontally
Factors Affecting Drop Size
Standard drop size 50ul (0.05ml)
Rapid bleeding gives slightly larger drop
Shaking/movement casts off smaller drops Breaks surface tension
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Shape & Size of Bloodspot
- Depends mostly on nature of target surface
- Texture (rough or smooth)
- Porous or non porous
- Angle of impact
- Size is also related to distance fallen
- Given a standard 50 ul drop of blood
- There is little change in spot diameter beyond a fall distance of 4 ft (1.2m)
Direction and Origin
- Point of Convergence
- Two dimensional
- Shows directionShows direction
- Point of Origin
- Three dimensional
- Shows direction and height
Point of Convergence
Point of Origin
length width Angle of impact = arc sin W/L oint of convergence^ (Parent Drop)
Origin
( p)
Distance from point of convergence
Height above p 85 ° 60 ° 45 ° 30 °
Tracing Origin of
Bloodspots
- Point of convergence method
- 2 dimensional; shows direction
- Point of origin method
- 3 dimensional; to include height
- In practice:
- use of string & protractor at scene
- use of computer at laboratory
Blood Spatter Velocity
- Low velocity (5 f/s, 1.5 m/s)
- Free-falling drops, cast off from weapon
- Medium velocity (25 - 100 f/s, 7.5 - 30 m/s)
- High velocity (>100 f/s, >30 m/s)
Low Velocity Blood Spatter
- Blood source subjected to LV impact
- Spot diameter: mostly 4 - 8 mm
- some smaller, some larger
- Free-falling drops (gravity only)
- Cast off from fist, weapon, etc.
- Dripping (blood droplets into themselves)
- Splashing (stepping, throwing, etc.)
- Arterial spurting
Cast-off from Weapon
- First blow causes bleeding
- Subsequent blows contaminate weapon with blood
- Blood is cast-off at a tangent to arc of upswingg p g or backswing (90 degrees)
- Pattern & intensity depends on:
- type of weapon
- amount of blood adhering to weapon
- length of arc, swing
Downswing of Hammer
Cast-off from Weapon
ceiling
Overhead swing with bloodied metal bar
Cast-off Pattern (1/2)
Direction?
Cast off Pattern (2/2)
Direction? (^) 1
2
3
Dripping Pattern
- Free-falling drops dripping into wet blood
- Falling from a stationary object
- Large irregular central stain
- Small round & oval satellite stains
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Drip 1:Drip 1:
Blood dripping into itself from height of 1 m (8 drops) Notice Irregular Central Stain
DripDrip 1: 1:
Drip 2Drip 2
Blood dripping into itself from height of 1 m (8 drops) Closer View Showing Round and Oval Satellite Stains
pp
Splash Pattern
- Volume > 1 ml
- Subjected to LV impact
- Thrown
- Tipped
- Large central irreg lar area s rro ndedLarge central irregular area surrounded by elongated peripheral spatter pattern
Splash 1Splash 1
5 ml blood squirted from a syringe from a height of 1m
Splash 2Splash 2
5 ml blood squirted from a syringe from a height of 1 m (Closer View of Central Stain)
Splash 3Splash 3
5 ml blood squirted from a syringe from a height of 1 m
(Closer View of Peripheral Stains) Direction? Splashing on a vertical
surface
10 ml blood thrown 1 m
6” ruler
onto a vertical surface
Stamp 1Stamp 1
Blood pool (10 drops) before stamping
Stamp 2Stamp 2
Blood pool (10 drops) after stamping with shoe
Arterial Spurt Pattern
- Blood exiting body under arterial pressure (120 mm Hg); corresponds to heart beating
- Large stains with downward flow on vertical surfaces; air bubbles present if lung was punctured
- Creates a wave-like appearance
Arterial Spurt Pattern
High Velocity Blood Spatter
- Blood source subjected to HV impact
- Fine mist: spot size < 0.1 mm
- Small mass limits spread to 1 m
- Some larger droplets reach further
- Gunshot
- back-spatter from entry wound
- forward spatter from exit wound
- High speed machinery
Gunshot: Back & Forward Spatter
Bloodstained foam held just above target surface.
bullet
Bullet passing L to R just above sheet
Bullet enters foam
bullet exits foam
Back spatter on entry
Forward spatter on exit
Gunshot Back Spatter
- Arises from entrance wound
- Passes back towards weapon & shooter
- Seen only at close range of fire
- SSeen on:
- inside of barrel
- exterior of weapon
- hand, arm, chest of shooter
Back spatter
on
steadying
hand
Gunshot Forward Spatter
- Arises from exit wound
- Passes forward in same direction as shot
- More copious than back-spatter
- Can be seen at any range of fire
- Seen on nearby surfaces, objects, persons
- especially on wall behind victim
Forward spatter (5 ms after bullet impacted at 1000 f/s)
bullet
blood soaked target
Forward spatter on a target (15cm from exit point) due
to a HV impact (bullet)
6” ruler
Forward Spatter (closer view to show misting)
Forward Spatter (closest view) Droplet Size 0.1mm
5 mm
Other Patterns
- Bloodstain patterns that have been altered
- Altered by objects, gravity, others
- Include:• Include:
- Wipe Patterns
- Swipe Patterns
- Transfer Patterns
- Flow Patterns
Wipe and Swipe Patterns
- Wipe
- Object moves through a wet bloodstain
- Removes and/or alters bloodstain appearance
- Does not require a swipe pattern be present
- Swipe
- Transfer of blood to an unstained surface
- Direction may be determined by feathered edge
- A wipe pattern must also be present
Transfer Patterns
- Wet, bloodied object contacts a secondary surface
- Transfer from:
- hand, fingers
- shoes, weapon
- hair
- Transfer to:
- walls, ceilings
- clothing, bedding
- Produces mirror-image of bloodied object
