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Chapter 8 Blood and Blood Splatter Introduction and History

Chapter 8 Blood and Blood Splatter Introduction and History. Blood typing can provide class evidence; whereas DNA profiling can provide individual evidence. A blood splatter pattern can give information about the truthfulness of an account by a witness or a suspect.

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Chapter 8 Blood and Blood Splatter Introduction and History

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  1. Chapter 8 Blood and Blood SplatterIntroduction and History • Blood typing can provide class evidence; whereas DNA profiling can provide individual evidence. • A blood splatter pattern can give information about the truthfulness of an account by a witness or a suspect. • It also can provide information about the origin of the blood, the angle and velocity of impact, and type of weapon used. • Our understanding of blood began in ancient times and continues to grow today. Forensic Science: Fundamentals & Investigations, Chapter 8

  2. Composition of Blood • Whole blood carries cells and plasma—the fluid Shown above respectively: • Red blood cells carry oxygen to the body’s cells and carbon dioxide away. • White blood cells fight disease and foreign invaders and, alone, contain cell nuclei. • Platelets aid in blood clotting and the repair of damaged blood vessels. Forensic Science: Fundamentals & Investigations, Chapter 8

  3. Blood Typing—Proteins 42% 12% 3% 43% of the population in the United States (of which 85% is Rh+) • Blood typing is quicker and less expensive than DNA profiling. • It produces class evidence but can still link a suspect to a crime scene or exclude a suspect. Forensic Science: Fundamentals & Investigations, Chapter 8

  4. Blood Typing—Antibodies; Additional Proteins and Enzymes • Antibodies are proteins secreted by white blood cells that attach to antigens to destroy them • Antigens are foreign molecules or cells that react to antibodies • *More info on blood typing, antibodies and antigens will be given in a future lesson. Forensic Science: Fundamentals & Investigations, Chapter 8

  5. Blood Splatter • In 1939 the meaning of the splatter pattern was first analyzed. • When a wound is inflicted, a blood splatter pattern may be created. • It takes a grouping of blood stains to make a blood splatter pattern. • The pattern can help to reconstruct the events surrounding a shooting, stabbing, or beating. Forensic Science: Fundamentals & Investigations, Chapter 8

  6. Blood Splatter Analysis Analysis of a splatter pattern can aid in determining the: • direction blood traveled. • angle of impact. • point of origin of the blood. • velocity of the blood. • manner of death. Forensic Science: Fundamentals & Investigations, Chapter 8

  7. Blood Splatter Analysis • When blood falls from a height or at a high velocity, it can overcome its natural cohesiveness and form satellite droplets. • When it falls onto a less-than-smooth surface, it can form spiking patterns around the drops. Forensic Science: Fundamentals & Investigations, Chapter 8

  8. Blood Splatter Analysis—Impact Patterns can help investigators determine the type of weapon used. • Observe the differences in the spatter produced by the gun (left) as opposed to the hammer (right) Forensic Science: Fundamentals & Investigations, Chapter 8

  9. Blood Splatter Analysis—Directionality The shape of an individual drop of blood provides clues to the direction from where the blood originated. Forensic Science: Fundamentals & Investigations, Chapter 8

  10. Blood Splatter Analysis—Location of the Origin of the Blood Lines of convergence • Draw straight lines down the axis of the blood splatters. • Where the lines converge, the blood originated. Forensic Science: Fundamentals & Investigations, Chapter 8

  11. Crime Scene Investigation of Blood • Search for blood evidence. • If any is discovered, process it determining: • Whether the evidence is blood. • Whether the blood is human. • The blood type. • Interpret the findings: • See if the blood type matches a suspect. • If it does not, exclude that suspect. • If it does, decide if DNA profiling is needed. Forensic Science: Fundamentals & Investigations, Chapter 8

  12. Review Questions – 10 Formal Points • What information can blood spatter analysis provide investigators? • What is “whole blood”? • Describe the difference between red and white blood cells. • What are platelets? • What are the four classes of Blood type and how common is each in the United States? • What is the difference between antibodies and antigens? • How do satellite droplets form? • How do spiking patterns form? • What can the shape of an individual blood droplet reveal to the investigator? • How do you draw lines of convergence and what can they reveal to an investigator?

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