Blood stains
Collection/Preservation of Blood Evidence
• Secure scene
• Alert EMT/Medical personnel to
preserve clothing (e.g. bullet holes,
knife holes in clothing)
• Photograph bloodstains/document
before removing stains
• Maintain Chain of Custody – who has
handled the evidence
2
Blood Evidence
• To collect blood from a movable item
– Keep on item (if small – e.g. clothes, money, etc)
– Make sure blood is DRY – if wet, must AIR DRY
– Package in paper bag
• Sealed bag with tape sign initial and date
• For unmovable items
– Dried stain - Use a sterile swab with sterile
distilled water to swab the bloodstain(s)
– Allow to air dry before storage
• Place in sealed paper envelope/bag
3
Types of “wet” blood evidence
• Fresh, liquid blood
– Use a disposable pipette and transfer to a
purple top tube with EDTA
• Whole blood from a living person
– Whole blood from the victim and suspect is
collected at autopsy or by medical
professionals in a purple top tube with
EDTA
4
Blood Evidence cont.
• Use purple-top EDTA tubes ONLY for
DNA/Serology analysis; EDTA preserved
the DNA
– When refrigerated, blood in EDTA is good
for approx 3-5 days
• When whole blood arrives at the crime
lab, make a standard bloodstain as soon
as possible
5
Examples of Dried Blood Stains
• Crusts of dried blood – Scrape into a clean
paper envelope or scrape into paper, then
fold paper and place into paper envelope
• Stained knives/rocks – submit the item
without sampling – make sure knives are
secured
• Upholstery/rugs – Cut out section and submit
to lab – Also collect an unstained portion for
a control sample
6
Dried Blood Stains - continued
• Stains on walls: small stains – Photograph
First - Moisten a cotton swab with water
then rub stain with swab – use more than
one swab if needed – If possible allow to
air dry and place cotton swab in paper
envelope
• Submit a control cotton swab with only
water
• Large stains – Photograph First – Scrape
blood into paper envelope or use swabs to
collect blood and follow procedure for
small stains
7
Collection of Blood Evidence
• Clothing – if wet with blood or other body
fluid, allow to air dry naturally before it is
sealed and brought to laboratory
• If identification marks are made, make sure it
is away from stained area
• Package all clothing in paper bags – DO NOT
PUT IN PLASTIC! – Medical staff will do this –
Re-package when at the police department
• Do not shake out clothing. If on floor in a
pile – indicate order and package each item
individually.
8
Blood Evidence
• How many swabs do you collect and where
do you collect them?
– At the discretion of the crime scene technician or
individual in charge of scene
– Evaluate scene and determine which stains are
crucial to the case
– Limited opportunity to collect stains
– If there are many stains collected, understand the
crime lab will not run every sample – determine
which samples need to be analyzed
9
10
Step 1 FIND POSSIBLE BLOOD STAINS
11
Step 1 FIND POSSIBLE BLOOD STAINS
Bloodstain Pattern Analysis
• Blood stains can provide valuable evidence that can
support or refute information given by witnesses or
suspects.
• It can also provide an investigator with a crime scene
interpretation as to where and how an impact
occurred, how many blows and from what sort of
weapon.
12
Step 1 FIND POSSIBLE BLOOD STAINS
Bloodstain Pattern Analysis
• Blood spattering is common in the scene
of any injury.
• The injury of artery cause blood spattering
is easy to understand.
• In most time, blood either falls or is thrown
off often depend on some active
movement.
13
Step 1 FIND POSSIBLE BLOOD STAINS
DIFFERENT SHAPES OF BLOOD SPATERING
IN DIFFERENT SPEED ,ANGLE AND VOLUME
14
Step 1 FIND POSSIBLE BLOOD STAINS
• Through the analysis the patterns of blood
stains, we can determine the origin of splash
and the movement of victim after he/she was
wounded.
15
Step 1 FIND POSSIBLE BLOOD STAINS
Blood
Spatter
• Blood drops form different shapes and sizes
• Blood spatter analysis uses the shapes and
sizes to reconstruct the crime scene.
16
Step 1 FIND POSSIBLE BLOOD STAINS
Blood Spatter (speed)
• Faster drop = larger diameter (size)
• Higher distance = larger diameter
17
Step 1 FIND POSSIBLE BLOOD STAINS
Blood Spatter (volume)
• size of drop also depends on the volume of
the drop.
• Volume depends on object blood originated
from (needle = small; bat = large)
18
Step 1 FIND POSSIBLE BLOOD STAINS
Blood Spatter (Effect of Surface)
• Smooth surface = smooth sphere
• Rough/porous surface may cause some
splatter
19
Step 1 FIND POSSIBLE BLOOD STAINS
Determining Direction of Blood
• Narrow end of a blood drop will point in the
direction of travel.
20
Step 1 FIND POSSIBLE BLOOD STAINS
Determining Direction of Blood
If more than one drop (from spatter) results, the
point of origin can be determined
21
Step 1 FIND POSSIBLE BLOOD STAINS
Determining Direction of Blood
If more than one drop (from spatter) results, the
point of origin can be determined
22
Step 1 FIND POSSIBLE BLOOD STAINS
Types of blood stain
There are four main categories of blood stain types:
• Patterns - identifiable patterns in blood such as
footprints or fingerprints
• Smears -identifiable patterns that show movement
• Pools -area where blood has statically collected.
These can show whether a body has been moved
• Spattered -provide the most information about the
incident
23
Step 1 FIND POSSIBLE BLOOD STAINS
Types of Spatter—Spattered Blood
• Spattered Blood = random distribution of
bloodstains that vary in size
• Amount of blood and amount of force affect the
size of blood spatter.
• Can result from gunshot, stabbing, beating
24
Step 1 FIND POSSIBLE BLOOD STAINS
Types of Spatter—Spattered Blood(continue)
• Help determine the location of the origin of the
blood source.
• Help determine the mechanism which created
the pattern.
25
Step 1 FIND POSSIBLE BLOOD STAINS
Types of Spatter—Spattered Blood(continue)
• In general, for higher impacts, the pattern is
more spread out and the individual stains are
smaller.
 Low impact = beating
 High impact = gunshot
26
Step 1 FIND POSSIBLE BLOOD STAINS
Types of Spatter—Gunshot Spatter
• Gunshot Spatter = can result in a mist-like
spatter that indicates a gunshot.
• Not all gunshots will result in misting.
• If misting is present, it is most likely a gunshot.
27
28
Step 2 PRILIMINARY TEST OF BLOOD STAINS
Preliminary test —Purposes
• To exclude the materials that conclusively not
blood stains quickly in order to centralize our
works on real blood stains .
29
Step 2 PRILIMINARY TEST OF BLOOD STAINS
Preliminary test —Principals
Hemoglobin
deoxidize phenolphthalein
(have peroxidase activity )
H2O2
(colorless)
[O]
H2O
phenolphthalein (red color)
Negative result
(With no color reaction)
Positive result
(with color reaction)
30
Step 2 PRILIMINARY TEST OF BLOOD STAINS
Preliminary test —Result Analysis 1
• Negative result indicating:
• No blood materials in the sample
( because the test is very sensitive)
• Disposition of sample when the test
shows negative result:
• To cast off !
31
Step 2 PRILIMINARY TEST OF BLOOD STAINS
Preliminary test —Result Analysis 2
• Positive result indicating:
•There maybe some blood materials in the sample
(because the test is sensitive, everything that
has peroxidase activity should show positive result)
• Disposition of sample when the test shows positive result:
To save for the following analysis
32
Step 2 PRILIMINARY TEST OF BLOOD STAINS
Preliminary test —methods
• Benzidine
• Leucomalachite green
Phenolphthalein
• Luminol and Spectrophotometric
tests
33
Benzidine blood stain
34
Luminol reacts with the iron in haemoglobin in a
chemiluminescent reaction to emit blue light
35
36
Step 3 Conclusive TEST OF BLOOD STAINS
Conclusive test —Purposes
To make sure the materials to be studied are real
blood stains
37
Step 3 Conclusive TEST OF BLOOD STAINS
Conclusive test —Principals
正铁血红素
血红素
变性珠蛋白
38
Step 3 Conclusive TEST OF BLOOD STAINS
Conclusive test —Result Analysis 1
• Negative result indicating:
• 1. No blood materials in the sample
• 2. Minutes blood materials maybe in the sample
( because the test is insensitive)
• Disposition of sample when the test shows
positive result:
• To save for the following analysis
39
40
Step 4 SPECIES TEST OF BLOOD STAINS
Species test —Purposes
• To distinguish human from these animals
41
Step 4 SPECIES TEST OF BLOOD STAINS
Species test —Principals
42
Step 4 SPECIES TEST OF BLOOD STAINS
Species test —precipitation reaction
• Precipitation
– Soluble Ab + soluble Ag
– Divalent Ab molecules crosslink multivalent Ag to form a lattice
– Ag-Ab complex reaches a certain size and loses its solubility and
precipitates out of solution
– Precipitin curves are based on the amount of Ag-Ab complexes
precipitated
• Zone of Ab excess
• Zone of equivalence
• Zone of Ag excess
43
Step 4 SPECIES TEST OF BLOOD STAINS
Species test —precipitation reaction
44
Step 4 SPECIES TEST OF BLOOD STAINS
Species test — Result Analysis 1
• Negative result indicating:
• Samples must not be human blood materials
( because the test is very sensitive)
• Disposition of sample when the test shows
negative result:
• To determine which kinds of animals blood
materials if necessary.
45
Step 4 SPECIES TEST OF BLOOD STAINS
Species test — Result Analysis 2
• Positive result indicating:
• The sample must be human blood materials!
(because the test is very specific)
• Disposition of sample when the test shows
positive result:
• To save for the following analysis
46
Step 4 SPECIES TEST OF BLOOD STAINS
Species test —method
47
Step 4 SPECIES TEST OF BLOOD STAINS
Laboratory Analysis
• If it is blood, is it
Human Blood?
Confirmatory tests for
human blood
• ABH HemaTrace cards
• Species Identification
tests (Ouchterlony
Gel)
胶体金试验
48
49
Step 5 INDIVIDUAL IDENTIFICATION OF BLOOD STAINS
Individual identification — overview
• The key task of forensic medicine science is to grasp
the criminals!
• So to find characters of criminals is most important.
• Individual identification can provide biological
characters of criminals!
• Concluding: personal (or individual) identification
is the key process of blood stains test!
50
Step 5 INDIVIDUAL IDENTIFICATION OF BLOOD STAINS
51
Step 5 INDIVIDUAL IDENTIFICATION OF BLOOD STAINS
Individual identification —blood groups
• Absorption test
• Elution test
52
Step 5 INDIVIDUAL IDENTIFICATION OF BLOOD STAINS
blood groups —Elution test
• 1. antiserum of the various blood types added to stain
• 2. wash off uncombined antiserum
• 3. break the bond between antibodies and antigen heating to
56 degrees C.
• 4. have only antibodies which have combined with antigens
on the blood stain. Mix these antibodies with red blood
cells of known types
• 5. Agglutination of the known cells
Sensitive enough to type a stain single fiber one-half inch
long.
Stains as old as 11 years
53
Blood Enzymes and Proteins
•Enzymes – Proteins that act as catalysts for
certain specific chemical reactions in the body.
•Polymorphism – The existence of more than one
form of a genetic trait.
•Iso-enzymes – Multiple molecular forms of an
enzyme, each having the same or very similar
enzyme activity.
54
Separation of PGM Iso-enzymes
Accomplished by Electrophoresis
55
Individual identification —DNA level
56
To link a stain to an individual
• Comparing known samples with unknown samples
– Crime scene sample
– Victim reference sample (blood tube or buccal swab)
– Suspect reference sample (blood tube or buccal swab)
• Reference sample should be a primary standard –a sample taken
from the person: pulled hairs, buccal swab, blood tube – taken by
medical staff or at autopsy
• Reference samples can not be blood from his/her shirt, blood off
floor by victim, which is a secondary standard
57