Chapter 8 Blood and Blood Splatter Introduction and

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

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

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

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

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

Blood Splatter 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. 6 Forensic Science: Fundamentals & Investigations, Chapter 8

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

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

Blood Splatter Analysis—Location of the Origin of the Blood l l 10 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

Crime Scene Investigation of Blood 1. Search for blood evidence. 2. If any is discovered, process it determining: a. Whether the evidence is blood. b. Whether the blood is human. c. The blood type. 3. Interpret the findings: a. See if the blood type matches a suspect. b. If it does not, exclude that suspect. c. If it does, decide if DNA profiling is needed. 11 Forensic Science: Fundamentals & Investigations, Chapter 8

Review Questions – 10 Formal Points What information can blood spatter analysis provide investigators? 2. What is “whole blood”? 3. Describe the difference between red and white blood cells. 4. What are platelets? 5. What are the four classes of Blood type and how common is each in the United States? 6. What is the difference between antibodies and antigens? 7. How do satellite droplets form? 8. How do spiking patterns form? 9. What can the shape of an individual blood droplet reveal to the investigator? 10. How do you draw lines of convergence and what can they 1. 12