bloodstains testing composition of blood plasma: fluid component – water (90%) – plasma proteins...
TRANSCRIPT
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Bloodstains Testing
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Composition of Blood
• Plasma: Fluid component– Water (90%)– plasma proteins– Other solutes
• Formed elements: Cells and fragments– erythrocytes (red blood cells)– leucocytes (white blood cells) – Platelets
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Bloodstains
• Wet blood has more value than dried blood because more tests can be run.
– Blood begins to dry after 3 – 5 minutes of exposure to air.
– As it dries, it changes color towards Brown or black.
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Nature of Blood Evidence
• Blood/Bloodstains may be encountered as physical evidence in:
– Homicides– Sexual Assault– Vehicular hit-and-run– Burglary– Other crimes
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"Every Contact Leaves a Trace".
Dr. Edmond Locard
Blood at the Scene is the most visible example of the Locard Exchange Principle
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血痕检验的目的和要求
Is this stain blood?
Human blood?Animal blood ?
Whose blood?SuspectVictim
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Process of Blood Testing
Visual inspection
Presumptive test
Confirmatory tests
Species-origin test
Individual Identification Paternity Testing
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Location Color Shape Area
Visual inspection
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Luminol
This chemical is used by crime scene investigators to locate traces of blood, even if it has been cleaned or removed.
Investigators spray a luminol solution is throughout the area under investigation and look for reactions with the iron present in blood, which causes a blue luminescence.
Luminol Reaction
How is blood evidence detected at a crime scene?
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Luminol Testing
Luminol will give false reactions.
• One problem is that other substances also react, such as some metals, paints, cleaning products, and plant materials.
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Luminol Testing
Studies have shown that luminol will cause the loss of several genetic markers.
– Another problem is that the chemical reaction can destroy other evidence in the crime scene.
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Luminol Testing
Because Luminol is so sensitive to bloodstains, it is occasionally used to enhance bloody impressions (shoeprint, fingerprint, etc).
• Not the best method however, because it is water-based. This could cause loss of valuable information from a bloodstain.
First choice should be high intensity light.
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Light SourceInvestigators will first examine the crime scene to look for areas that may contain blood.
They may use a high-intensity light or UV lights to help them find traces of blood as well as other bodily fluids that are not visible under normal lighting conditions.
How is blood evidence detected at a crime scene?
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For small/movable item——collect the whole object
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For big /immovable evidence ——scraping , shearing , cutting , wet transferring , tape Lifting
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Label
Case file number
Description of the biological evidence(type, number, color , location and so on)
The date and time of picking up the evidence
The place of picking up the evidence
The person who pick up the evidence——signature
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Each item of evidence must be packaged separately and labeled with accurate tag
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The characteristics of biological evidence from crime scenes
Biological evidence
The changement of the environment(high temperature 、 rain 、
strong sunlight 、 microbe degradation and so on)
denaturation 、 degradation 、 corruption
Correct collection 、 storage and test as soon as possible
How to store biological evidence
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The storage of Biological evidenceBody fluid(blood, urine, saliva and so
on )
Refrigeration(4℃or -20℃) or made stain
Air dried in shadow and
cool
Less than one week: 4 ℃
More than one week: 20 ℃
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Presumptive test
Sensitive
Rapid
特异性低
Simple
Less amount
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Blood – Presumptive testsBased on the peroxidase properties of hemoglobin
globin
heme
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Common Presumptive Tests
phenolphthalin (Kastle-Meyer)leucomalachite green (LMG)Luminol (BlueStar)3,3’,5,5’-Tetramethylbenzidine (TMB)leucocrystal violet (LCV)o-tolidineBenzidine: Carcinogenico-toluidinehydrogen peroxide: Bubbles
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Blood Reagent TestsThese tests, referred to as presumptive tests, are used to detect blood at crime scenes based upon the properties of hemoglobin in the blood. Further tests at the crime lab can determine if it is human blood or not.
Examples:
• Phenolphthalein is a chemical that is still utilized today and is usually referred to as the Kastle-Meyer test and produces a pink color when it reacts with hemoglobin.
•HemaStix is a strip that has been coated with tetramethylbenzidine (TMB) and will produce a green or blue-green color with the presence of hemoglobin.
Kastle-Meyer TestVideo
HemaStix
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Blood – Presumptive testsGeneral Considerations
heme has peroxidase activity
2H2O2
2O· + 2H2O
Heme Fe+++
Oxygen free radicals
cleaved from peroxide group
Heme Fe++
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Blood – Presumptive testsGeneral Considerations
Free radicals interact with organic chemicals (dyes)
O· chemical oxidized
Presumptive test detects oxidized organic dyes
+ Chemical reduced
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Kastle-Meyer Test
RareSome substances inhibit reactionBlood can mask the color changeAcidic solutions can mask the reaction
false negatives
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Benzidine
• • The benzidine test is used for many years but
has been discontinued because the reagent is carcinogenic.
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Presumptive test
(-) Not blood or blood destroied
stop
(+)May be blood
GO
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Confirmatory tests
Possible bloodstains Definite bloodstain
Specific
灵敏度低
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Takayama test
操作简便、结晶清晰,但高山试剂久置易失效,每次试验时应当用已知血痕作阳性对照,且灵敏度低。
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Confirmatory tests
(-)Not Blood( Less or Destroied )
stop
(+)Blood
GO
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Species-origin test
Species-origin
Human Bloodstains
Animal BloodstainsBloodstains
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加 样 区 反 应 区 吸 附 区
检测线抗人 Hb抗体
为 Ig
质控线抗 Ig抗体为抗 Ig
包被免疫胶体金的玻璃纤维
膜
硬质塑料底板
吸水滤纸
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Human BloodCross-reaction with Ferret BloodAnti-human Hemoglobin
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Human BloodCross-reaction with Ferret BloodAnti-human Hemoglobin
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Species-origin test
(-)Animal (+)Human
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Visual inspection
Presumptive test
(-)不是血(或已破坏)(+)可能是血
Confirmatory tests
(-)不是血(量太少或已破坏) (+)肯定是血
Species-origin test
Bloodstain Testing
(-)不是人血 (+)是人血
Individual Identification Paternity Testing