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Blood Spatter. Is it blood? Is it human? How did it get there?. Is it blood?. Kastle-Meyer test Phenophthalein + hydrogen peroxide Hemoglobin acts as peroxidase —accelerates oxidation with peroxide Presumptive : potatoes and horseradish also give a positive test. Molecule flattens out

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blood spatter

Blood Spatter

Is it blood?

Is it human?

How did it get there?

is it blood
Is it blood?
  • Kastle-Meyer test
    • Phenophthalein + hydrogen peroxide
    • Hemoglobin acts as peroxidase—accelerates oxidation with peroxide
    • Presumptive: potatoes and horseradish also give a positive test

Molecule flattens out

-bond conjugation leads to

color

other blood tests
Other Blood Tests
  • Hemastix (sold to identify blood in urine)
    • Wet stain with distilled water
    • Rub stain with swab
    • Rub swab on Hemastix
    • Turns green in presence of blood
    • Does not interfere with subsequent DNA testing
other blood tests4
Other Blood Tests
  • Luminol
    • Extremely sensitive—luminesces blue
    • Detectable after 300,000 X dilution
    • Does not interfere with DNA tests later
    • Interferences from bleach, copper, horseradish
luminol chemistry
Luminol Chemistry

Catalyzed by Fe

in hemoglobin

Light is emitted

other blood tests7
Other Blood Tests
  • Microcrystalline tests
    • Teichmann—NaCl+acetic acid
    • Takayama--pyridine

hematin

is it human
Is it human?
  • The overall strategy
    • Use animal hosts to make specific antibodies that react with species specific blood proteins (antigens)
    • Antibodies and antigens both have multiple sites that can react with each other

Antibody

Antigen

is it human9
Is it human?
  • Precipitin test
    • Rabbit injected with human or other blood to make specific antibodies
    • Rabbit blood serum isolated
      • Has antibodies to specific species injected
    • Visible precipitin line formed if matching antibody and antigen meet
      • Test tube, gel, gel electrophoresis
what makes one liquid different from another
What makes one liquid different from another?
  • Density
    • 1.035 g/mL for blood
  • Viscosity
    • Plasma 1.3X water
    • Blood 2.4X plasma = 3.1X water
  • Blood is a suspension
size and shape of drops
Size and Shape of Drops
  • Determined by
    • Velocity
    • Direction
    • Distance from point of origin
    • Texture of surface
  • Higher the impact energy, the smaller the droplets
    • Drops are large (> 3 mm)
    • Impact spatter from beating and knife attacks are medium sized (> 1 mm)
    • Spatter from gunshot wounds, machinery, sneezes is fine (< 1mm)
texture of surface
Texture of Surface

Smooth Surface

Textured Surface

http://brazoria-county.com/sheriff/id/blood/bloodspatter_general.htm

forces acting on drops
Forces Acting on Drops
  • Gravity
    • Projectile motion
      • Causes parabolic trajectory in vertical direction
  • Viscosity
  • Surface Tension
    • Droplet is a sphere in flight
angle of impact
Angle of Impact

http://www.bergen.org/EST/Year5/images/splatterangle.jpg

angle of impact17
Angle of Impact

http://home.iprimus.com.au/ararapaj/craigslea_testbed/Forensic%20Web%20Test%20Site/blood_spatter_analysis.htm

angle of impact18
Angle of Impact
  • Tail of drop points in direction of travel
  • Proper length of ellipse is symmetric about widest point

http://en.wikipedia.org/wiki/Blood_pattern_analysis_at_crime_scenes

angles from origin
Angles from origin
  •  angle from vertical
  • sin  = width/length
  • tan  = tan /sin 
volume of convergence
Volume of Convergence
  • Obtained from long axis of ellipse
  • 2-D convergence
  • Height obtained from shape of ellipse

http://home.iprimus.com.au/ararapaj/craigslea_testbed/Forensic%20Web%20Test%20Site/blood_spatter_analysis.htm