blood stains 2 collection/preservation of blood evidence secure scene alert emt/medical personnel to...

Blood stains

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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

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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

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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

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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

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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

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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

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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.

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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

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Step 1 FIND POSSIBLE BLOOD STAINS

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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.


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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.


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DIFFERENT SHAPES OF BLOOD SPATERINGIN DIFFERENT SPEED ,ANGLE AND VOLUME


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• 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.


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Blood Spatter


• Blood drops form different shapes and sizes

• Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

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Blood Spatter (speed)


• Faster drop = larger diameter (size)

• Higher distance = larger diameter

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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)


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Blood Spatter (Effect of Surface)


• Smooth surface = smooth sphere

• Rough/porous surface may cause some splatter

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Determining Direction of Blood


• Narrow end of a blood drop will point in the direction of travel.

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If more than one drop (from spatter) results, the point of origin can be determined

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If more than one drop (from spatter) results, the point of origin can be determined


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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

Types of blood stain


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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

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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.

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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

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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.

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Preliminary test —Purposes

• To exclude the materials that conclusively not blood stains quickly in order to centralize our works on real blood stains .

Step 2 PRILIMINARY TEST OF BLOOD STAINS

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Preliminary test —Principals


Negative result

(With no color reaction) Positive result

(with color reaction)

Hemoglobin

(have peroxidase activity )

deoxidize phenolphthalein

(colorless)

H2O2 [O]

H2O phenolphthalein (red color)

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• 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 !


Preliminary test —Result Analysis 1

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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

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• Benzidine• Leucomalachite green

Phenolphthalein• Luminol and Spectrophotometric

tests


Preliminary test —methods

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Benzidine blood stain

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Luminol reacts with the iron in haemoglobin in a chemiluminescent reaction to emit blue light

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Conclusive test —Purposes

Step 3 Conclusive TEST OF BLOOD STAINS

To make sure the materials to be studied are real

blood stains

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Conclusive test —Principals


正铁血红素血红素

变性珠蛋白

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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


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Species test —Purposes

• To distinguish human from these animals

Step 4 SPECIES TEST OF BLOOD STAINS

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Species test —Principals


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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


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Species test —precipitation reaction


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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.


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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


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Species test —method


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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

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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!

Step 5 INDIVIDUAL IDENTIFICATION OF BLOOD STAINS

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Individual identification —blood groups

• Absorption test

• Elution test


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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


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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.

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Separation of PGM Iso-enzymes Accomplished by Electrophoresis

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Individual identification —DNA level

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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

blood stains 2 collection/preservation of blood evidence secure scene alert emt/medical personnel to...

Documents

scrape blood

edtawhole blood

etcmake sure blood

living personwhole blood

crime scene technician

paper envelopesubmit

sterile swab

clean paper envelope