Press F5 on the keyboard to start the slideshow
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3.8: BLOOD TESTS & SPATTER
ANALYSIS
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- Luminol - The most sensitive chemical test
that is capable of presumptively detecting bloodstains diluted up to 300,000 times.
- It’s reaction with blood emits light and thus requires the result to be examined in a darkened area
1. Latent bloodstains at crime scenes
- Excellent search technique for:
2. Those scenes where it is suspected that attempts were made to clean bloodstains from an area
- Applied by a spraying technique
- Wide areas can be efficiently searched for blood
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- Luminol
- Reacts with an oxidizing agent – iron in hemoglobin
- Lasting about 30 seconds
- Results in a striking blue glow
- Drawbacks:
- Not specific to blood
- Can also be triggered by copper, certain bleaches, trace amounts of blood in urine, fecal matter, and animal blood
- Further confirmation of blood species testing and ultimately DNA testing is essential
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http://www.smithsonianchannel.com/sc/web/series/1003122/catching-killers/3375551/blood-spatter#blood-spatter-101 The link above contains a short video.Click on the one that looks like this:
Before clicking on the link above, please insert your headphones/earbuds.
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Useful to detect drugs in blood and urine.
Combine the drug with a protein and inject it into an animal (rabbit), the drug-protein complex acts as an antigen to which the animals antibodies react
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-Serology: study of antigen-antibody reactions
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*Used to determine if blood is of human or animal origin
*Animals are injected with human blood and the animal produces antibodies and forms a precipitate
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What questions must be asked when examining dried blood?
1. Is it blood?
2. What species did the blood originate?
3. Is it human blood?
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*Color test used to detect blood
*Phenolphthalein used
*Mix=blood +phenol.+ hydrogen peroxide
*Result=blood produces pink color because of oxidation of hemoglobin
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1) Origin(s) of bloodstain2) Distance of bloodstain from target3) Direction from which blood impacted
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4) Speed with which blood left its source5) Position of victim & assailant6) Movement of victim & assailant7) Number of blows/shots
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On average, blood accounts for 8 % of total body weight
5 to 6 liters of blood for males 4 to 5 liters of blood for females
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A 40 percent blood volume loss, internally or/and externally, is required to produce irreversible shock (death).
A blood loss of 1.5 liters, internally or externally, is required to cause incapacitation.
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http://www.smithsonianchannel.com/sc/web/series/1003122/catching-killers/3375551/blood-spatter#blood-spatter-101 The link above contains a short video.Click on the one that looks like this:
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Experiments with blood have shown that a drop of blood tends to form into a sphere in flight rather than the artistic teardrop shape.
The formation of the sphere is a result of surface tension that binds the molecules together.
This elastic like property of the surface of the liquid makes it tend to contract.
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More rapid bleeding may result in slightly larger drops.
BUT, on the contrary, slower bleeding does not result in smaller drops.
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Blood cast from a moving source will tend to consist of smaller droplets.
Blood behaves as a projectile in motion and obeys the laws of physics and mathematics.
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“Fitting” of an ellipse in blood drop
Tail or spine
Parent Drop
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PASSIVETRANSFERPROJECTED
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DEFINITION: drops created or formed by the force of gravity acting alone.
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EXAMPLES:
DropsDrip Patterns
PoolsClots
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“Passive” PICTURES:
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DEFINITION: created when a wet, bloody surface comes in contact with a secondary surface.
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EXAMPLES:
Contact bleeding Swipe or Smear
Wipe Smudge
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“Transfer” PICTURES:
A recognizable image of all or a portion of the original surface may be observed in the pattern.
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DEFINITION: created when an exposed blood source is subjected to an action or force, greater than the force of gravity.
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EXAMPLES:
Arterial Spurt / GushCast-Off
Impact Spatter
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“Projected” PICTURES:
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Low VelocityMedium Velocity
High Velocity
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LOW VELOCITY
Relatively large stains 4mm in size and greater. Gravitational pull up to 5 feet/sec.
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MEDIUM VELOCITY
Preponderant stain size 1 to 4mm in size.
Force of 5 to 25 feet/sec.
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HIGH VELOCITY
Preponderant stain size 1mm or greater. Force of 100 feet/sec. or greater.
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The spherical shape of blood in flight is important for the calculation of the angle of
impact (AOI) of blood spatter when it hits a surface.
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When a droplet of blood strikes a surface perpendicular (90 degrees) the resulting bloodstain will be circular. That being the length and width of the stain will be equal.
90○ ANGLE
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Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.
70○ ANGLE
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45○ ANGLE
30○ ANGLE
10○ ANGLE
5○ ANGLE