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CRIME SCENE RECONSTRUCTION: FORENSIC BLOODSTAIN PATTERN ANALYSIS

CRIME SCENE RECONSTRUCTION: FORENSIC BLOODSTAIN PATTERN ANALYSIS. Crime Scene Reconstruction.

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CRIME SCENE RECONSTRUCTION: FORENSIC BLOODSTAIN PATTERN ANALYSIS

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  1. CRIME SCENE RECONSTRUCTION: FORENSIC BLOODSTAIN PATTERN ANALYSIS

  2. Crime Scene Reconstruction • The method used to support a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident, is referred to as reconstruction. • Crime-scene reconstruction relies on the combined efforts of medical examiners, criminalists, and law enforcement personnel to recover physical evidence and to sort out the events surrounding the occurrence of a crime. BLOODSTAIN ANALYSIS

  3. Stain Patterns of Blood • The crime scene investigator must remember that the location, distribution, and appearance of bloodstains and spatters may be useful for interpreting and reconstructing the events that produced the bleeding. • Surface texture and the stain’s shape, size, and location must be considered when determining the direction, dropping distance, and angle of impact of a bloodstain. FORENSIC SEROLOGY

  4. Stain Patterns of Blood • Surface texture is of paramount importance. In general, the harder and less porous the surface, the less spatter results. • The direction of travel of blood striking an object may be discerned because the pointed end of a bloodstain always faces its direction of travel. • The impact angle of blood on a flat surface can be determined by measuring the degree of circular distortion. At right angles the blood drop is circular, as the angle decreases, the stain becomes elongated. • The origin of a blood spatter in a two-dimensional configuration can be established by drawing straight lines through the long axis of several individual bloodstains. The intersection or point of convergence of the lines represents the origin point. BLOODSTAIN ANALYSIS

  5. Stain Patterns of Blood • A shooting may leave a distinct gunshot spatter pattern. This may be characterized by both forward spatter from an exit wound and back spatter from an entrance wound. • The location of injury, the size of the wound created, and the distance between the victim and the muzzle of the weapon all affect the amount of back spatter that occurs. • A cast-off pattern is created when a blood-covered object flings blood in an arc onto a nearby surface. • Arterial spray spatter is created when a victim suffers an injury to a main artery or the heart. Commonly, the pattern shows large spurted stains for each time the heart pumps. BLOODSTAIN ANALYSIS

  6. Stain Patterns of Blood • A pattern created by blood that is expelled from the mouth or nose from an internal injury is called an expirated blood pattern. • A void is created when an object blocks the deposition of blood spatter onto a target surface or object. • When an object with blood on it touches one that does not have blood on it, this produces a contact or transfer pattern. • Examples of transfers with features include fingerprints, handprints, footprints, footwear prints, tool prints, and fabric prints in blood. • Patterns made by drops or large amounts of blood flowing by the pull of gravity are called flows. BLOODSTAIN ANALYSIS

  7. Stain Patterns of Blood • A pool of blood occurs when blood collects in a level (not sloped) and undisturbed place. • The edges of a stain will dry to the surface, producing a phenomenon called skeletonization. • A trail pattern is a series of drops that are separate from other patterns, formed by blood dripping off an object or injury. BLOODSTAIN ANALYSIS

  8. Documenting Bloodstain Evidence • Investigators should note, study, and photograph each pattern and drop of blood to accurately record the location of specific patterns and to distinguish the stains from which laboratory samples were taken. • The investigator should create photographs and sketches of the overall pattern to show the orientation of the pattern to the scene. • Two common methods of documenting bloodstain patterns are the grid method and the perimeter ruler method. BLOODSTAIN ANALYSIS

  9. Figure 12-1 A laser beam is used to determine the search area for the position of a shooter who has fired a bullet through a window and wounded a victim. The bullet path is determined by lining up the victim’s bullet wound with the bullet hole present in the glass pane.

  10. Figure 12–7  Illustration of stain convergence on a two-dimensional plane. Convergence represents the point from which the stains emanated. Courtesy Judith Bunker, J. L. Bunker & Assoc., Ocoee, FL

  11. REVIEW QUESTIONS (1-5) • Why is the surface texture of paramount importance in the interpretation of bloodstain patterns? • How can an investigator tell the direction of travel of blood from the shape of a bloodstain? • What is the difference between the shape of a bloodstain that impacts a surface at a low angle and one that impacts at a higher angle? • What is the difference between forward spatter and back spatter? Which is more likely to be deposited on the object or person creating the impact? • In general, as both the force and velocity of impact increase, what happens to the diameter of the resulting blood droplets?

  12. REVIEW QUESTIONS 6-13 • Why might investigators overlook some high-velocity spatter? • Define the terms area of convergence and area of origin and explain what kind of information each reveals to an investigator. • Name three factors that affect the amount of backward spatter produced by a gunshot wound. • What is the drawback effect? How is it helpful to an investigator? • What determines the size of blood drops in a cast-off pattern? Explain. • What is expirated blood? Name two ways to distinguish expirated blood from other types of bloodstains. • What is a void pattern? How might a void pattern be useful to investigators? • What is a transfer pattern? How is a simple transfer pattern created?

  13. REVIEW QUESTION 14-18 • How does the first transfer pattern in a series differ from subsequent ones? • What is a flow pattern? What should one surmise if a flow found on an object or body does not appear consistent with the direction of gravity? • How can pools of blood aid in reconstructing a crime scene? • Explain how the shape of stains in a trail pattern can help investigators determine the direction and speed at which a person was moving. • Name and describe two methods for documenting bloodstain patterns.

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