Questions and Answers
Describe how to find the area of convergence.
The area of convergence is the point on a two-dimensional plane from which the drops in an impact pattern originated. This can be established by drawing straight lines through the long axis of several individual bloodstains, following the line of their tails.
Describe how to find the area of origin.
The area of origin of an impact bloodstain pattern is the area in a three-dimensional space from which the blood was projected. This will show the position of the victim or suspect in space when the stain-producing event took place.
Which is 2D: the area of convergence or area of origin?
Which is 3D: the area of convergence or area of origin?
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You can calculate the angle at which a blood spatter impacts a surface.
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What formula do you use to find the angle of impact?
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When calculating the angle of impact, does the bigger number always go on the top or on the bottom of the equation?
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The impact angle of blood on a flat surface can be determined by measuring the degree of circular distortion.
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How do you discern the direction of travel of blood?
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When blood is dropped at a right angle to a surface, what shape will it be?
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How does the shape of a blood droplet/stain change as the angle decreases?
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When does an impact spatter occur?
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What is impact spatter?
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What is forward spatter? How does it occur?
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What is another name for back spatter?
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What information can be gathered from droplet size at a crime scene?
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What can not be found or deduced by impact patterns?
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Describe a low velocity spatter: size and distance of travel.
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Describe a medium velocity spatter: size and distance of travel.
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Describe a high velocity spatter: size and distance of travel.
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What are the limitations of impact spatter and how should they be used?
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What causes impact spatter?
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What action(s) causes impact spatter?
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When does cast-off spatter occur?
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What action causes arterial spurt pattern?
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Give example(s) of what creates high impact spatter.
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Give examples of what creates medium impact spatter.
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Give examples of what creates low impact spatter.
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Which type of spatter (low, medium or high velocity) will travel the furthest from the source of blood?
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Describe the differences between impact, forward and back spatters.
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What is drawback spatter?
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What kind of spatter do you see with a gunshot? (3 types and 1 velocity)
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Which will cause larger cast-off spatter, a baseball bat or a knife?
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Give examples of items that cause cast-off patterns.
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Can you determine the exact number of blows that were made by looking at cast-off spatter patterns?
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Name the features that affect the cast-off patterns.
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What causes a cast-off spatter?
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How does the color from an arterial blood spatter differ from other spatters?
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How do you identify the site of the initial injury when an arterial blood spatter is present?
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What is arterial blood spatter?
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What is void spatter?
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Void spatter is the most common type of bloodstain pattern found at a crime scene.
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What causes a void spatter?
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What can a void spatter tell a crime scene investigator?
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What is an expirated blood pattern? Where does it come from?
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What is the significance of expirated blood pattern at a crime scene?
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Where does expirated blood come from?
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How is expirated blood different in color from other spatters?
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What is skeletonization and how does it occur?
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What does the skeletonization time indicate to an investigator?
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How long does it typically take for skeletonization to occur?
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What is a contact/transfer pattern?
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Is a swipe pattern a type of transfer pattern?
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What is a flow pattern?
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What can flow patterns show?
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What can interruption of flow pattern tell a crime scene investigator?
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What is a pool pattern?
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What happens to the size of a pool pattern when it's on an absorbent surface?
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What can the drying time of a blood pool tell a crime scene investigator?
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What is the difference between a drip pattern and drip trail?
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What is a drip trail pattern?
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What can a drip or drop trail pattern tell a crime scene investigator?
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What is a blood swipe?
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What is blood wipe?
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What are blood swipe patterns?
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How does the diameter of a blood drop pulled down only by gravity change as height changes?
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How can you tell the direction a blood drop was traveling?
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True or False: Blood that falls on glass will have less splatter than blood that falls on a soft surface.
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Study Notes
Bloodstain Pattern Analysis
- The area of convergence determines where blood droplets originated by intersecting their tails in a 2D plane.
- The area of origin provides a 3D perspective on where blood was projected, helping establish positions during an incident.
- The angle of impact can be calculated using the formula: Sin A = Width of blood stain / Length of blood stain, where the larger number is the denominator.
- Blood stains at a right angle are circular, while elongated stains indicate a shallower angle of impact.
- Impact spatter is produced when an object strikes a blood source, resulting in outward projection of blood droplets.
Types of Spatter
- Forward spatter ejects blood away from the source, while back spatter (or blow-back spatter) moves towards the source.
- Cast-off spatter occurs when a blood-covered object flings blood in an arc after striking something.
- Arterial spurt patterns arise from a punctured artery, producing large spurts with each heartbeat.
Spatter Velocity Classification
- Low velocity spatter (4 mm diameter or larger) results from impacts under 5 ft/sec.
- Medium velocity spatter (1-4 mm diameter) occurs from impacts between 5 to 25 ft/sec.
- High velocity spatter (less than 1 mm diameter) results from impacts over 100 ft/sec.
Cast-off Patterns
- Sizes of cast-off spatter vary between blunt objects (larger drops) and sharp objects (smaller drops).
- The number of blows can be inferred from the count and arrangement of spatter patterns.
- Factors influencing cast-off patterns include object size, blood amount, and movement direction.
Distinctive Blood Patterns
- Void patterns indicate an absence of blood where an object or person obstructed blood deposition.
- Expirated blood patterns come from blood expelled from injuries to the mouth or nose, often appearing bright due to bubbles.
- Flow patterns depict blood movement influenced by gravity, deducing the position or movement of individuals involved.
Drip Patterns
- Drip patterns consist of blood falling drop-by-drop, while drip trails show movement over time, potentially indicating direction and suspect identity.
- Skeletonization occurs when blood edges dry within approximately 50 seconds, preserving an outline of the original stain.
Surface Interaction
- Blood stains differ based on the surface; harder surfaces produce less spatter, while softer surfaces may exhibit more dispersion.
- Stain size increases with height due to gravitational effects, affecting blood diameter upon impact.
Key Observations
- The pointed end of a blood stain indicates its direction of travel.
- Understanding the color variation in arterial blood spatter provides clues about the type of injury sustained.
- Blood wipes occur when a moving object alters a bloodstain, indicating interaction with the existing pattern.
These bullet points encapsulate crucial information from the material on bloodstain pattern analysis, allowing for efficient study and review.
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Description
Test your knowledge of bloodstain pattern analysis, focusing on concepts like area of convergence, area of origin, and different types of spatter. This quiz will challenge your understanding of how to interpret blood evidence at a crime scene.