1 BLOOD

2 Introduction and History Blood typing can provide class evidence Using DNA from blood is individual evidence Blood spatter patterns provide information about the origin of the blood, the angle and velocity of impact, and type of weapon used

3 Composition of Blood Whole blood carries cells and plasma—the fluid with hormones, clotting factors, and nutrients. 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.

4 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.

5 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.

6 Blood Typing—Probability and Blood Types By identifying the additional proteins in the blood evidence sample, investigators can limit the size of a suspect population and help identify a suspect. For example: What is the chance of throwing dice and getting two sixes?

7 BR What are the four blood types and their percentages in the population?

8 Science of Murder clip

9 Use of luminol to find blood stains that are no longer visible to the naked eye. Luminol reacts with hemoglobin to produce a blue glow. The brighter and stronger the glow, the fresher the blood.

10 Blood Spatter In 1955, blood spatter analysis was first used in a courtroom to free Sam Sheppard (The Fugitive). When a wound is inflicted, a blood spatter pattern may be created. A grouping of blood stains is a blood spatter pattern. The pattern can help to reconstruct the events surrounding a shooting, stabbing, or beating.

11 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.

12 The next slide contains a strong image. Feel free to turn you head

13 OJ Simpson crime scene

14 Blood Spatter Blood is a mixture of blood cells and plasma It is cohesive – meaning it sticks together Maintains a circular shape

15 Blood Drop Characteristics Although blood drops remain circular, they can have satellites or spikes Parts of the blood that separate from the main drop are called satellites Spikes remain attached to the large drop

16 satellite spikes

17 Blood dropped from different heights

18 Blood Spatter Analysis—Six Patterns Describe each of these: a. passive drops b. arterial gushes c. splashes d. smears e. trails f. pools

19 Blood Spatter Analysis—Impact Patterns can help investigators determine the type of weapon used. The faster the blow, the smaller the drops

20 Types of Injury High velocity (gunshot) Medium velocity (hammer strike) Low velocity ( drip)

21 Blood Spatter 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?

22 Determining direction of travel

23 Wave Cast-off. Parent drop wave cast-off Tail of wave cast-off points back to parent drop Tail of elongated stain points in direction of travel

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26 Dexter movie clip

27 Location of the Origin of the Blood Lines of convergence Draw straight lines down the axis of the blood spatters. Where the lines converge, the blood originated.

28 Lines of Convergence Draw line through the axis of the main droplet Start at the end of the blood drop and draw toward the source Do not draw lines through satellite drops Draw smallest circle around intersection -marks point of convergence

29 Points of Convergence The red circle shoes the point of convergence.

30 Point of Convergence

31 Angle of Impact length width Angle of impact = arc sin W/L Distance from point of convergence Height above point of convergence Origin 85  60  45  30 

32 Angle of Impact Take the inverse sin of width/length

33 Determine Angle of Impact WidthLengthsinearc sine ° ° ° Hand-out

34 The point where the lines of spatter connect is called the point of convergence. This shows where the blood came from, which is where the victim was at the time of the attack. In the diagram to the right, strings were used to determine the point of convergence. Wherever the strings connect is where the spatter came from (where the victim was).

35 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.

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 spatter evidence can be used to recreate a crime scene. Investigators endeavor to (a) locate, (b) identify, and (c) interpret blood spatter patterns at crime scenes.