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Introduction to Bloodstain Pattern Analysis “Art in the blood is liable to take the strangest forms.” Sir Arthur Conan Doyle (1893) Sherlock Holmes, The Adventure of the Greek Interpreter Objectives At the end of this lesson, students should be able to… ⚫ Define bloodstain pattern analysis (BPA) and its associated terms ⚫ Explain why BPA is a useful forensic tool ⚫ Describe the physical characteristics of blood ⚫ Know the different types of bloodstain patterns ⚫ Discuss how to document and collect bloodstain evidence ⚫ Understand the limitations of pattern recognition and the limitations of BPA as a science What is Bloodstain Pattern Analysis? Bloodstain Pattern Analysis (BPA) The science that uses the physical appearance and spatial distribution of static bloodstains to establish a timeline of the events that lead to their deposition What is Bloodstain Pattern Analysis? Primary Functions of BPA: 1. To define or categorize specific stains and patterns found at a crime scene 2. To attempt to identify the nature of the events that caused the patterns Unlike other types of evidence, bloodstain patterns can provide information about what happened at a crime scene Why is BPA Useful as a Forensic Tool? The shape of an individual stain indicates the angle of impact Bloodstains vary in shape and size The size of an individual stain indicate the force used to create that stain As the force exerted on a blood source increases, the resulting stains are smaller and more spread out Why is BPA Useful as a Forensic Tool? Analysts look at stains collectively and evaluate the patterns with respect to each other Helps to indicate the relative positioning of the suspect, victim, and other related objects during the incident Distribution of bloodstains Example: Was the victim standing up or lying on the floor when he was attacked? Why is BPA Useful as a Forensic Tool? Experiments! Blood behaves similarly under the same type of circumstances Bloodstains are reproducible Why is BPA Useful as a Forensic Tool? Once outside of the body, blood obeys certain predictable physical laws Conducting experiments can help provide a variety of information about the incident that occurred. Types of Information: Amount and type of force; approx. number of blows struck; positioning of persons involved; mechanism that created the pattern; etc. Physical Characteristics of Blood • Volume • Shape and surface tension • Impact on a target surface What Can Bloodstains Tell Us? The volume of a drop of blood in flight will always remain the same What Can Bloodstains Tell Us? Blood droplets will not break up spontaneously during flight Drops of blood will retain their shape until acted upon by some other force The size of a drop of blood is dependent on its volume Click on photo to link to video clip. Physical Characteristics of Blood As a result of surface tension, a blood droplet retains a spherical shape while in flight Physical Characteristics of Blood The liquid is forced to occupy a sphere (smallest space possible) because the surface tension (molecular bonding force) on the surface of the droplet is stronger than the bonding force within the mass of liquid Damping is the process by which a blood droplet in flight stabilizes almost immediately Physical Characteristics of Blood The target surface is the most critical element involved in the appearance of the resulting stain Physical Characteristics of Blood The distortion of a stain may eliminate an analyst’s ability to decipher anything of value from the blood evidence For example, blood on carpet or fabric is absorbed by the surface, distorting the stain Smooth surfaces produce the best bloodstain patterns What Can Bloodstains Tell Us? • Directionality • Angle of Impact • Area of Origin • Distance What Can Bloodstains Tell Us? Directionality: The direction a blood drop was traveling at the time it impacted a surface What Can Bloodstains Tell Us? Inertia caused by the motion of the droplet forces a wave of blood to form, which then wells up on the opposite point from where the stain struck the surface The leading edge of the blood droplet impacts first and the blood runs in the direction of travel The tail of the bloodstain always points in the direction of travel What Can Bloodstains Tell Us? Inertia caused by the motion of the droplet forces a wave of blood to form, which then wells up on the opposite point from where the stain struck the surface The leading edge of the blood droplet impacts first and the blood runs in the direction of travel The tail of the bloodstain always points in the direction of travel What Can Bloodstains Tell Us? Angle of Impact: The angle at which a blood drop strikes a surface What Can Bloodstains Tell Us? The greater the angle of impact, the more circular the resulting bloodstain. What Can Bloodstains Tell Us? The greater the angle of impact, the more circular the resulting bloodstain. What Can Bloodstains Tell Us? Area of Origin: The approx. area above the target surface from which the drop originated What Can Bloodstains Tell Us? 3D location in space – the stains radiate out from the area of origin What Can Bloodstains Tell Us? Distance: The approx. distance above the target surface where the stain originated What Can Bloodstains Tell Us? Helps to determine the location of the origin of the blood source Due to air resistance, terminal velocity for a drop of blood occurs at a distance of approx. 7 feet You can only determine conclusively the distance a drop of blood has fallen if you know the volume of the drop Bloodstain Pattern Categories • Passive • Transfer • Projected or impact • Types of force • Miscellaneous Bloodstain Pattern Categories Drops, flows, pools, and clots Passive Stains Provides information about when the bloodshed occurred and any disturbances that happened after the bloodshed Bloodstain Pattern Categories Drop: Often referred to as passive bleeding or low velocity spatter Click on photo to link to video clip. Bloodstain Pattern Categories The more quickly a blood source is moving, the greater the distance between the drops of blood The tails on drops of blood can tell the direction in which the actively dripping blood source was moving at the time of deposition Satellite spatter result from the deposition of small droplets that are ejected from the blood pool when it’s struck by a falling drop Click on photo to link to video clip. Bloodstain Pattern Categories Passive Flow: Created by gravity alone, and does not involve circulatory action Blood Pool: Pattern occurs when gravitational forces pull blood to the lowest possible level, and the blood accumulates Bloodstain Pattern Categories The blood flow takes the path of least resistance Helps to indicate whether items at a crime scene have been moved Saturation stains occur when a surface absorbs a quantity of blood Bloodstain Pattern Categories Clot: Blood that has undergone the physiological process of fibrin formation that congeals the solid elements of blood into a gelatinous mass Bloodstain Pattern Categories Patterns, swipes, and wipes Result when a bloody object comes into contact with another surface Transfer Stains Provides info about: • Movement of the victim or suspect • Sequence of events • Identification of weapons Bloodstain Pattern Categories Pattern Transfer: Created when a wet bloody object comes into contact with another surface Bloodstain Pattern Categories The resulting pattern may provide specific characteristics that help to identify the object Bloodstain Pattern Categories Swipe: Results when a bloody object comes into contact with a clean surface Provides indication of movement within the crime scene Bloodstain Pattern Categories Wipe: Results when a non-bloody object comes into contact with a bloody surface Provides indication of movement within the crime scene *** this wipe also has skeletonization *** Bloodstain Pattern Categories Projected blood, spatter, castoff, and splashes Projected & Impact Stains Provides info about: • Type or nature of force used • Staging of scene • Min. number of blows (blunt force) • Movement of the victim Bloodstain Pattern Categories Projected Blood: Produced when blood, released under pressure, impacts a surface Bloodstain Pattern Categories Normally associated with arterial spurts and gushes – traumatic bleeding from vessels under pressure – and typically has a linear pattern Bloodstain Pattern Categories Spatter: The result of force being applied to a blood source Bloodstain Pattern Categories The greater the force, the smaller the resulting blood drops, and the wider the distribution of the resulting stains Spatter is distributed randomly, varies in size, and is produced by a variety of mechanisms Types of Force Size: 4mm or larger Low Velocity: Results from normal gravitational force of up to 5 feet/sec. Typical of venus bleeding (blood under low pressure) Types of Force The size of the blood spatter is relatively large, because the energy applied to the blood source is limited, minimizing the degree to which the blood drops break apart Blood stains are often associated with blood dripping from an injury or weapon Types of Force Size: Approx. 1mm to 4mm Medium Velocity: Results from force or energy between 5 and 25 feet/sec. Typical of injuries resulting from blunt force trauma Types of Force Blood droplets are broken up as a result of increasing energy applied to the blood source Typically associated with beatings and stabbings Bloodstain Pattern Categories Cast-Off: Created when blood is flung or projected from an object in motion, or when that motion stops suddenly Bloodstain Pattern Categories Arc cast-off patterns are characterized by linear patterns, typically found on the ceiling or walls The objects casts off blood droplets as it arcs through the air Cessation/stop-action cast-off patterns are created by a bloodbearing object is stopped abruptly Bloodstain Pattern Categories The directionality of castoff patterns in relation to the area of origin may provide information about which hand the offender used during the attack May be used (with caution) to estimate a minimum number of blows in blunt force trauma Help to reconstruct the series of events and locations of those involved Types of Force Size: Mist-like; 1mm or smaller High Velocity: Results from force or energy in excess of 100 feet/sec. Typical of gunshot wounds, high powered machinery injuries, and explosions Types of Force Bullet hole Types of Force Bullet hole Back spatter are bloodstains that are projected towards the item creating the force or energy. For example, when a bullet is fired from a gun and hits a bloody surface, blood not only travels in the direction of the bullet, but also travels backwards onto the gun. Bloodstain Pattern Categories Expirated Blood: Blood which is spattered on a target from the mechanical process of breathing Bloodstain Pattern Categories Expirated blood accumulates in the lungs, sinuses, and airway, and may be mixed with saliva or nasal secretions These stains often include air bubbles. Because expirated blood tends to form a fine mist due to the pressure exerted by the lungs moving air out of the body, it may be mistaken for high velocity spatter Bloodstain Pattern Categories Splash: Pattern created when a volume of blood impacts a surface with minimal force Bloodstain Pattern Categories Typically associated with a staged crime scene, where blood has been poured on a surface Bloodstain Pattern Categories Voids, skeletonization, and expirated blood Miscellaneous Stains Provides info about: • Movement at the scene • Timing of events • Sequence of events Bloodstain Pattern Categories Voids: An empty space found in the middle of an otherwise bloody surface Bloodstain Pattern Categories Voids are useful for determining the positioning of items during the event. For example, a void may be indicative that a door was open during the attack or that an item is missing from the scene. Bloodstain Pattern Categories Fly Spots: Regurgitation, excretion, or tracking of minute amounts of blood around a scene or onto items a within the scene Bloodstain Pattern Categories May be mistaken for spatter, but is not actually a result of the bloodshed Bloodstain Pattern Categories Skeletonization: Occurs when a blood stain, which has begun to dry, is disturbed Bloodstain Pattern Categories Blood dries from the outside inward, so when an object goes through a bloodstain that is still wet, the skeleton of the stain remains. Drying time is dependent upon the surface on which the blood is deposited and the environmental conditions Documentation and Collection Limitations of BPA Documentation and Collection Photography and sketches Follow standard crime scene processing procedures to locate and adequately document all blood evidence Stringing Documentation and Collection Photographs: It is critical to take the close-up photographs at a 90° angle to the evidence to avoid distortion Scales Bloodstain Photo taken from 90° angle Documentation and Collection Sketches: Cross-projection sketches are most useful because bloodstain scenes need to be viewed in more than one dimension Documentation and Collection Cross-projected sketches are helpful in showing the relationships between various groups of stains. These stains exist on different surfaces, including objects in the room, floors, walls, and the ceiling Documentation and Collection Stringing: Used to provide a graphic 3D illustration of the areas of origin of bloodstains Documentation and Collection Practically speaking, stringing is useful for determining whether a victim was standing, lying down, or sitting in a chair when the bloodshed occurred It is important to remember that stringing is not an exact science, and only provides an estimation of the area of origin Limitations of BPA Requires significant experience and training Ability to interpret bloodstains Ability to provide effective testimony in court Analysis should not be conducted with a limited number of stains Information available through BPA is dependent upon the circumstances found at a crime scene The greater the number of stains, the greater the potential for accurate assessment of the scene The messier the crime scene, the more information that is available to analysts Limitations to Pattern Recognition Environmental Factors Post-Event Artifacts Quality of Scene Information Ancillary Information Temperature Offender activity Photographs Medical and/or autopsy reports Humidity Medical intervention on scene Measurements Lab reports Civilian and first responder activity Control of scene Individual statements (suspect, victim, etc.) Animal and insect activity Press reports Limitations to Pattern Recognition Environmental Factors Post-Event Artifacts Quality of Scene Information Ancillary Information Temperature Offender activity Photographs Medical and/or autopsy reports Humidity Medical intervention on scene Measurements Lab reports Civilian and first responder activity Control of scene Individual statements (suspect, victim, etc.) Animal and insect activity Press reports BPA only provides parameters for the investigator – there are few absolutes in bloodstain pattern interpretation