what is forensic science? forensic science is the application of science to the law. it often...
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What is forensic science?
• Forensic Science is the application of science to the law.
• It often involves police officers and scientists from many branches of science working as a team to solve a crime.
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How did Forensic Science catch their killer?
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How did Forensic Science catch How did Forensic Science catch their killer?their killer?
1. Why do you think it is important that ‘Most forensic scientists are not police officers’?
2. The evidence in this case was collected from 4 major sites – can you name them?
3. How long did it take the Forensic Science Service to process all the evidence?
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Investigating Blood Spatter
Patterns
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Categories of blood stainsCategories of blood stains
• Blood patters can be roughly grouped into 3 categories:
• Passive
• Transfer
• Projected
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PassivePassive
These are drops created only by the force of gravity.
They can be further subdivided into
•Drops
•Drip patterns
•Pools
•Clots
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TransferTransfer
• These occur when a wet, bloody surface contacts another surface. This may lead to a recognisable footprint or hand/fingerprint.
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ProjectedProjected• This is where the source of bleeding is
subjected to another force – e.g. a blow or sudden movement. The size and shape of the drops produced depends on the size of the force.
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What else can affect the patterns?What else can affect the patterns?
• The amount of blood
• The surface it lands on
• The height it drops from
• The direction it comes from
Blood on glass – no distortion
Blood on linoleum – distortion of edges
Blood on wood – lots of distortion
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• Low velocity (1.5 m/s)– e.g. free-falling drops, cast off from
weapon
• Medium velocity (7.5 - 30 m/s)– e.g. baseball bat blows
• High velocity (>30 m/s)– e.g. gunshot, machinery
Types of Blood SpatterTypes of Blood Spatter
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Investigating blood patternsInvestigating blood patterns
• Your task is to carry out an investigation to see if the height that blood drips from (passive) affects how big the droplets are.
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Blood patterns resultsBlood patterns results
Height (M) Size of drop (mm)
Size of drop (mm)
Average size of drop (mm)
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What is Forensic Science all about?
• Anthropology• Ballistics• Crime• Entomology• Evidence• Fibres• Trace
• Fingerprints• Odontology• Insects• Serology• Toxicology• Pathology• All about SCIENCEAll about SCIENCE!
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Blood Spatter Analysis – extension higher ability
CSI
The origin is in the angle
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History
• 1894 - Pitorowski wrote earliest reference to bloodstain pattern analysis
• 1939 - Balthazard was first to use physical interpretations of stains
• 1955 - Dr. Paul Kirk used bloodstain pattern interpretation as a defense witness in the Sam Shepherd case
• 1971 - Professor Herbert MacDonnell promoted bloodstain pattern interpretation as a tool for modern criminalistics
• 1983 – The International Association of Bloodstain Pattern Analysis was formed
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Summary
What is Blood? Determining Distance of Blood Determining Direction of Blood Types of Blood Stain Patterns
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What is Blood?
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Introduction to Blood
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Blood Spatter (or splatter)
Blood drops form different shapes and sizes
Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.
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Determining Distance Blood Falls
Blood drops fall as small spheres
Blood Spatter > Distance
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Determining Distance Blood Falls
Drops form circle when hitting surface
Size depends on speed of blood drop
Blood Spatter > Distance
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Determining Distance Blood Falls
Faster drop = larger diameter (size)Higher distance = larger diameter
Due to air resistance, speed maxes out at distances above about 7 feet
Blood Spatter > Distance
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Determining Distance Blood Falls
However, size of drop also depends on the volume of the drop.
Volume depends on the object blood originated from (needle = small; bat = large).
Blood Spatter > Distance
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Determining Distance Blood Falls
Since the volume of blood is unknown…
The distance a drop has fallen cannot be measured.
Blood Spatter > Distance
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Effect of Surface
Smooth surface = smooth sphere Rough surface may cause some
splatter
Blood Spatter
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Determining Direction of Blood
Narrow end of a blood drop will point in the direction of travel.
Blood Spatter > Direction
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Activity - 1
• Obtain the blood solution, dropper, protractor and paper plate
• Drop one drop of blood from 3 feet above the plate with the plate at 90 degrees to the dropper (i.e. 0 degrees on the protractor)
• Drop 3 more drops in different locations but with each subsequent drop decrease the angle between the dropper and the plate and either take a picture or draw what you see
• Record the angles used and observe the drops • Describe what you see
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Angle (degrees)
Picture (Drawn or photographed) Picture observations
90 (0 on protractor)
Insert photo or drawing Describe in detail what you see
60 (30 on a protractor)
Insert photo or drawing Describe in detail what you see
30 (60 on a protractor)
Insert photo or drawing Describe in detail what you see
10 (80 on a protractor)
Insert photo or drawing Describe in detail what you see
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Conclusion
• Describe the relationship of angle of surface to blood pattern observed
• So angle angle of impact can be determined
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Angle of Impact“The tail tells the tale”
• 90 degrees –
• 60 degrees –
• 30 degrees –
• 10 degrees –
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Determining Direction of Blood
If more than one drop (from spatter) results, the point of origin can be determined
Blood Spatter > Direction
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Determining Direction of Blood
If more than one drop (from spatter) results, the point of origin can be determined
Blood Spatter > Direction
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Determining Direction of Blood
This is a 2-dimensional point of origin. It is possible to determine the 3-D point of
origin
Blood Spatter > Direction
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Determining Direction of Blood
The angle can be determined mathematically.
Width/Length, then take the inverse sin (sin-1).
This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle)
Blood Spatter > Direction
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For each blood drop, a string can be guided back to the point of origin.
Blood Spatter > Direction
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Activity 2 3D blood splatter
• Determine the 3D angle of our blood spattered wall and the position of our victim
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Types of Spatter
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
Blood Spatter
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Spattered Blood can:
Help determine the location of the origin of the blood source.
Help determine the mechanism which created the pattern.
Blood Spatter
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Spattered Blood
In general, for higher impacts, the pattern is more spread out and the individual stains are smaller.
Low impact = beating High impact = gunshot
Blood Spatter
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Types of 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.
Blood Spatter
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Gunshot Spatter
Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).
Blood Spatter
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Types of Spatter
Beating and Stabbing Spatter = larger individual stains
First blow usually doesn’t result in spatter since there is not yet any exposed blood.
Blood Spatter
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Types of Spatter
Satellite Spatter = free falling drops of blood that fall onto a spatter pattern.
These drips are usually much larger than impact spatter.
However, blood dripping into blood can create a spatter.
Blood Spatter
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Types of Spatter
Castoff Pattern = Blood flung off of swinging object.
Can reconstruct where assailant and victim were positioned.
Blood Spatter
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Types of Spatter
Expirated Bloodstain Pattern = Blood can accumulate in lungs, sinuses, and airway. Forcibly exhaled.
Can appear like beating or gunshot pattern.
May be mixed with saliva or nasal secretions.
Blood Spatter
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Alteration of bloodstain over time
Blood dries and clots over time. Difficult to estimate the time the blood
exited the body. Clotted smears can indicate time of
movement.
Blood Spatter
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• Blood analysis website
• Try to recreate some of these blood splatter patterns on A5 paper after reading through the website (without injuring any one please!!!!)
• You must consult your teacher when about to begin to ensure your safety
Activity 3