Forensic Science: Fundamentals & Investigations, Chapter 8 1 Chapter 8 Blood and Blood Splatter By the end of this chapter you will be able to: explain the composition of blood describe the function of blood cells determine the blood type of a blood sample conduct a blood splatter analysis examine wounds and describe the nature of the weapon find and process blood evidence All Rights Reserved South-Western / Cengage Learning © 2009

Forensic Science: Fundamentals & Investigations, Chapter 8 2 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. 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.

Composition of Blood Whole blood carries cells and plasma – Plasma—(55%) the fluid with dissolved proteins like antibodies, hormones, clotting factors, and nutrients like glucose, amino acids, salts and minerals. Forensic Science: Fundamentals & Investigations, Chapter 8 3

4 Composition of Blood Cellular components of blood (45%): Red blood cells carry oxygen to the body’s cells and carbon dioxide away, contain hemoglobin and no nucleus. White blood cells fight disease and foreign invaders and, alone, contain cell nuclei – used to make first DNA profile in 1982 Platelets are cell fragments that aid in blood clotting and the repair of damaged blood vessels.

Forensic Science: Fundamentals & Investigations, Chapter 8 5 The Composition of Blood Platelets - thrombocytes

Forensic Science: Fundamentals & Investigations, Chapter 8 6 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 7 Blood Typing—Antibodies; Additional Proteins and Enzymes Antibodies are proteins secreted by white blood cells that attach to antigens to destroy them (not made to attack our bodies own antigens). Antigens are substances on the cell surface of red blood cells (or foreign invaders) Enzymes are complex proteins that catalyze different biochemical reactions. Many enzymes and proteins have been found in the blood that are important for identification purposes.

Forensic Science: Fundamentals & Investigations, Chapter 8 8 Blood Types

Forensic Science: Fundamentals & Investigations, Chapter 8 9 Genetics - FUN STUFF!!!! Shows multiple alleles Shows codominance Genetics terms to know: – Genes – Traits – Alleles – dominant vs. recessive – Genotype – heterozygous vs. homozygous – Phenotype

Forensic Science: Fundamentals & Investigations, Chapter 8 10 Blood Typing—Probability and Blood Types Given the frequency of different genes within a population, it is possible to determine the probability that a particular blood type will appear in a particular population. To determine the probability of two separate events, it is necessary to multiply their individual probabilities. By identifying the additional proteins in the blood evidence sample, investigators can limit the size of a suspect population and help identify a suspect.

Forensic Science: Fundamentals & Investigations, Chapter 8 11 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 12 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 13 Blood Splatter Analysis When blood falls from a height or at a high velocity, it can overcome its natural cohesiveness and form satellite droplets (separates from the original). When it falls onto a less-than-smooth surface, it can form spiking patterns around the drops, if not it will have a curved surface due to surface tension with smooth edges Blood is cohesive Gravity causes a drop of blood to elongation as it falls

Forensic Science: Fundamentals & Investigations, Chapter 8 14 Blood Splatter Analysis—Six Patterns Describe each of these: a. passive drops b. arterial gushes c. splashes d. smears e. trails f. pools

Forensic Science: Fundamentals & Investigations, Chapter 8 15 Blood Spatter Analysis - Blood Drops Size & shape help identify the direction of origin – Round drops: 90 degree angle drop – Tails & Satellites: Indicate where the blood came from (points of origin) – Blood drops lead away from the source

Forensic Science: Fundamentals & Investigations, Chapter 8 16 Blood Splatter Analysis—Impact Patterns can help investigators determine the type of weapon used. – What kind of a pattern is produced by a gun shot? – What kind of a pattern is produced by a hammer blow? – Voids are used to indicate the presence of a person or object Fine Mist

Forensic Science: Fundamentals & Investigations, Chapter 8 17 Blood Splatter Analysis— Directionality The shape of an individual drop of blood provides clues to the direction from where the blood originated. How will the point of impact compare with the rest of a blood pattern? Points in the direction of movement

Forensic Science: Fundamentals & Investigations, Chapter 8 18 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 19 Crime Scene Investigation of Blood 1. Search for blood evidence. a. Luminol is used to detect the blood protein hemoglobin even after an area has been cleaned of blood it will react and generate light 2. If any is discovered, process it determining: a. Whether the evidence is blood. - (1) Kastle-Meyer test - turns pinks in the presence of blood or (2) Lukomlalachite green test -turns green in the presesnce of blood b. Whether the blood is human - ELISA test c. The blood type.

Forensic Science: Fundamentals & Investigations, Chapter 8 20 Crime Scene Investigation of Blood 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.

Forensic Science: Fundamentals & Investigations, Chapter Summary Summary Blood consists of cellular components and plasma. The various human blood types are caused by the presence or absence of A or B or both A and B proteins on the surface of red blood cells. Blood splatter evidence can be used to recreate a crime scene. Investigators endeavor to (a) locate, (b) identify, and (c) interpret blood splatter patterns at crime scenes.