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Chapter 8 Blood and Blood Spatter 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 spatter analysis examine wounds and describe the nature of the weapon find and process blood evidence All Rights Reserved South-Western / Cengage Learning © 2009 1 Forensic Science: Fundamentals & Investigations, Chapter 8 Genetic Terms to Remember 2 Phenotype- a set of observable characteristics of an individual Genotype- the genetic constitution of an individual Homozygous- having two of the same gene (either dominant or recessive) Heterozygous- having one dominant and one recessive copy of a gene Forensic Science: Fundamentals & Investigations, Chapter 8 Introduction and History Blood typing can provide class evidence; whereas DNA profiling can provide individual evidence. A blood spatter 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. 3 Forensic Science: Fundamentals & Investigations, Chapter 8 Composition of Blood Whole blood carries cells and plasma—the fluid 4 with hormones, clotting factors, and nutrients. 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 How do you get your blood type? There are 4 major blood types and 2 different antibodies: – – 5 A,B, AB, and O Anti-A and Anti-B You get your blood type from your parents. You can determine the possible blood types for an individual if you know the blood types of their parents. Forensic Science: Fundamentals & Investigations, Chapter 8 How do you get your blood type? 6 Your blood types is a phenotype, but some blood types can have multiple genotypes. Blood types A and B are dominant over O (recessive), but A and B are co-dominant with each other Phenotype Genotype Antibodies A AA or AO Anti-B B BB or BO Anti-A AB AB None O OO Anti-B and Anti-A Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Typing—Proteins 42% 12% 3% of the population in the United States (of which 85% is Rh+) 43% 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. 7 Forensic Science: Fundamentals & Investigations, Chapter 8 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. 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. 8 Forensic Science: Fundamentals & Investigations, Chapter 8 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. 9 Forensic Science: Fundamentals & Investigations, Chapter 8 Practice Probability 10 A man who is heterozygous Type A marries and woman who is heterozygous Type B. What are the possible phenotypes and genotypes of their children? Genotype Phenotype B O AB AB A AB AO AO A O BO OO BO B OO O Forensic Science: Fundamentals & Investigations, Chapter 8 The Rh Factor 11 Red blood cells carry proteins on their surfaces in addition to anti-A and anti-B. The Rhesus factor, Rh, is a protein carried by some individuals. If a person carries the Rh factor they are “Rh positive.” If not, they are “Rh negative.” Rh is a dominant trait, so only one copy of Rh+ is need for a person to be Rh+. Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis 12 http://www.youtube.com/watch?v=J40wqqg_ 8Ww Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter 13 In 1939 the meaning of the spatter pattern was first analyzed. When a wound is inflicted, a blood spatter pattern may be created. It takes a grouping of blood stains to make a blood spatter pattern. The pattern can help to reconstruct the events surrounding a shooting, stabbing, or beating. Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis Analysis of a spatter 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. 14 Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter 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. 15 Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis-Passive Patterns 16 Passive Drop- Bloodstain drop(s) created or formed by the force of gravity acting alone Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis-Passive Patterns 17 Drip Pattern- A bloodstain pattern which results from blood dripping into blood Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis-Passive Patterns 18 Flow Pattern- A change in the shape and direction of a bloodstain due to the influence of gravity or movement of the object Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis-Passive Patterns 19 Pool- a bloodstain pattern created when a source of blood remains stationary over a surface causing an accumulation of blood Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis-Passive Patterns 20 Saturation-A bloodstain pattern created when a volume of blood has been absorbed by an object Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis-Transfer Patterns 21 Transfer/Contact Pattern- a bloodstain pattern created when a wet, bloody surface comes in contact with a second surface. A recognizable image of all or a portion of the original surface may be observed in the pattern Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis-Transfer Patterns 22 Swipe Pattern-The transfer of blood from a moving source onto an unstained surface. Direction of travel may be determined by the feathered edge Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter Analysis-Transfer Patterns 23 Wipe Pattern- A bloodstain pattern created when an object moves through an existing stain, removing and/or altering its appearance Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter AnalysisProjected/Impact Spatter 24 Arterial Spurting- bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter AnalysisProjected/Impact Spatter 25 Cast-off Pattern- a bloodstain pattern created when blood is released or thrown from a blood-bearing object Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter AnalysisProjected/Impact Spatter 26 Expirated Blood- Blood that is blown out of the nose, mouth, or a wound as a result of air pressure and/or air flow which is the propelling force. Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter AnalysisProjected/Impact Spatter 27 Low Velocity Impact Spatter (LVIS)- A bloodstain pattern that is caused by a low velocity impact/force to a blood source Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter AnalysisProjected/Impact Spatter 28 Medium Velocity Impact Spatter (MVIS)- a bloodstain pattern caused by a medium velocity impact/force to a blood source. A beating typically causes this type of spatter Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter AnalysisProjected/Impact Spatter 29 High Velocity Impact Spatter (HVIS)- a bloodstain pattern caused by a high velocity impact/force to a blood source Often produced by a gunshot or high speed machinery Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter AnalysisMiscellaneous 30 Void- an absence of stain in an otherwise continue bloodstain pattern Indicates that a person or object was in the way of the blood spatter and was later moved Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Spatter AnalysisMiscellaneous 31 Skeletonized Stains- a bloodstain consisting of a darkened peripheral rim where the center of the stain is no longer intact 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. How will the point of impact compare with the rest of a blood pattern? 32 Forensic Science: Fundamentals & Investigations, Chapter 8 Blood Droplet Characteristics 33 A blood droplet will remain spherical in space until it collides with a surface. The spherical shape is caused by the surface tension of the blood. Forensic Science: Fundamentals & Investigations, Chapter 8 Angle of Impact The shape of a blood drop: – – 34 Round- if it falls straight down at a 90 degree angle Elliptical- blood droplets elongates as the angle decreases from 90 to 0 degrees Forensic Science: Fundamentals & Investigations, Chapter 8 Determining the Angle of Impact 35 Angle of impact= sin-1(width/height) Forensic Science: Fundamentals & Investigations, Chapter 8 Determining Angle of Impact 36 Make sure your calculator is in degrees! Example: Width= 3mm, Length= 5mm Angle= Sin-1(3mm/5mm) Angle = 37 degrees Forensic Science: Fundamentals & Investigations, Chapter 8 Origin of the Blood 37 Lines of convergence Draw straight lines down the axis of the blood spatters. Where the lines converge, the blood originated. Forensic Science: Fundamentals & Investigations, Chapter 8 Determining Point of Origin 1. 2. 3. 4. 5. 38 6. Place the ring stand on area of convergence Write the calculate angle of impact next to each stain. Using string, tape, and a protractor, raise the string to the calculated angle and attach it to the ring stand. Do the same for multiple stains. The place on the ring stand where the string from each stain meets is the area of orgigin Measure the height of the area of origin Forensic Science: Fundamentals & Investigations, Chapter 8 Crime Scene Investigation of Blood 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. 1. 39 Forensic Science: Fundamentals & Investigations, Chapter 8 . . . . . . . . . . . . . . . . . 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. 40 Forensic Science: Fundamentals & Investigations, Chapter 8