Bloodstains
Identification of blood, typing,
and splatter
3 questions about an
unknown stain
1.  Is it blood?
2.  From what species did the blood
originate?
3.  If the blood is of human origin, how
closely can it be associated to a
particular individual?
Is it Blood?
Preliminary Color Tests
1.  Benzidine Color Test - Benzidine is carcinogen
so not used as often
Benzidine + Blood Stain + Hydrogen peroxide
= pink color
2.  Kastle-Meyer Color Test -phenolphthalein
Phenolphthalein + Bloodstain + Hydrogen
peroxide = pink color
Is it Blood? (con.)
3.  Luminol Test - Reacts with blood to produce
luminescence
•
•
Sensitive to blood that have been diluted up to
10,000 times
Destroys many important blood factors
5.  Microcrystalline Tests - hemoglobin will form
characteristic crystals
•
less sensitive and more susceptible to
interference from contaminants
Luminol Test
Kastle-Meyer Test
Human or Animal origin?
Precipitin Test
•  Combine human antiserum and human bloodstain there
should be agglutination
•  Requires only small amount of blood
•  Dried bloodstains as old as 10 - 15 years work
Gel Diffusion
•  Human antibodies and bloodstain are placed in wells on an
agar gel. If antibodies and antigens move towards each other
and form a line of precipitation, it is human blood.
Electrophoretic Method
•  Similar to Gel diffusion except electrical current is used to
move antibodies and antigens towards each other
Matching blood to a person
1.  Blood type
2.  Blood Cell surface enzymes
3.  DNA Analysis
Blood Type basics
•  Four blood types - A
(39%), B (11%), AB (4%)
and O (46%)
•  Rh Factor -83% of
population are positive
•  Testing for blood type is
done through
agglutination and
antibodies
•  80% of the human
population are secretors
Typing blood
1.  Separately add A and B
antibodies to a few drops of
the blood sample.
2.  Look for agglutination.
3.  Agglutination will occur only
if the antigens are present
on the RBC.
4.  No agglutination with either
= O.
5.  Agglutination with both = AB
Typing of dried bloodstains
RBC rupture when they dry so agglutination tests
are not possible on dried blood stains
Absorption-Elution Technique - Four steps to
typing dried bloodstains
Step 1 - Place antiserum on bloodstain.
Step 2 - Wash off unreacted serum
Step 3 - Heat stained material to cause elution (breaking)
of antibody-antigen bond
Step 4 - Combine antibodies from bloodstain with known
RBCs. If agglutination occurs then the bloodstain can
be typed
Blood Enzymes and Proteins
•  Blood cells contain several different enzymes in
them that can be identified. The best enzymes
to identify for forensic purposes are those that
are polymorphic or have iso-enzymes
•  The more factors that are identified in a
bloodstain, the smaller its frequency of
occurrence.
•  Example: PGM (phosphoglucomutase) is found
in 10 different forms that
can be
isolated by electrophoresis.
Preservation of Blood Evidence
•  Photograph all blood close up and relative to the
entire crime scene.
•  Collection of all body fluids must be handled with
disposable gloves.
•  All clothing with blood on them should be
individually bagged and sent to the lab.
•  Bloodstains on substances that can not be
removed should be scraped off. A portion of the
surface near the stain should also be removed.
Bloodstains can also be removed using a swab
moistened with distilled water
Blood Splatter Rules
1.  Surface texture effects bloodstain patterns.
•
Harder and less porous the surface the less splatter.
2.  Direction of Blood’s travel may be shown by the stains
shape
•
Pointed end of a bloodstain always faces the direction it
traveled.
3.  It is possible to determine the impact angle of blood on a flat
surface by measuring the degree of circular distort.
•
Larger angles beyond 90 degrees the more elongated the stain.
4.  The origin of a Blood splatter can be established by drawing
straight lines through the long axis of several individual
bloodstains.
•
The point of convergence of the lines represents the point from which the
blood originated.
Different types of splatter
Angle of Impact
Blood at the scene
90 ˚ angle
Lack of splatter
The lack of splatter
can also indicate
what might have
happened at a
crime scene.
A person holding a
weapon, should not
have splatter where
the weapon was.