Blood Spatter

1
Blood Spatter

• Is it blood?
• Is it human?
• How did it get there?

2
Is it blood?

• Kastle-Meyer test
• Phenophthalein hydrogen peroxide
• Hemoglobin acts as peroxidaseaccelerates
  oxidation with peroxide
• Presumptive potatoes and horseradish also give a
  positive test

Molecule flattens out ?-bond conjugation leads to
color
3
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

4
Other Blood Tests

• Luminol
• Extremely sensitiveluminesces blue
• Detectable after 300,000 X dilution
• Does not interfere with DNA tests later
• Interferences from bleach, copper, horseradish

5
Luminol Chemistry
Catalyzed by Fe in hemoglobin
Light is emitted
6
Luminol at the Crime Scene
7
Other Blood Tests

• Microcrystalline tests
• TeichmannNaClacetic acid
• Takayama--pyridine

hematin
8
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
9
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

10
Precipitin Test
11
Precipitin Test
12
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

13
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 (gt 3 mm)
• Impact spatter from beating and knife attacks are
  medium sized (gt 1 mm)
• Spatter from gunshot wounds, machinery, sneezes
  is fine (lt 1mm)

14
Texture of Surface
Smooth Surface
Textured Surface
http//brazoria-county.com/sheriff/id/blood/bloods
patter_general.htm
15
Forces Acting on Drops

• Gravity
• Projectile motion
• Causes parabolic trajectory in vertical direction
• Viscosity
• Surface Tension
• Droplet is a sphere in flight

16
Angle of Impact
http//www.bergen.org/EST/Year5/images/splatterang
le.jpg
17
Angle of Impact
http//home.iprimus.com.au/ararapaj/craigslea_test
bed/Forensic20Web20Test20Site/blood_spatter_ana
lysis.htm
18
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_analysi
s_at_crime_scenes
19
Angles from origin

• ? angle from vertical
• sin ? width/length
• tan ? tan ?/sin ?

20
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_test
bed/Forensic20Web20Test20Site/blood_spatter_ana
lysis.htm