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Blood Evidence: Analyses, Types, and Patterns

Delve into the investigation of blood, its types, DNA analysis, serology, and splatter patterns in forensic science. Unravel the mysteries behind bloodstain shapes, impacts, and identifying human from non-human blood. Learn about serological testing methods and interpreting blood spatter patterns in crime scene investigations.

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Blood Evidence: Analyses, Types, and Patterns

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  1. Blood “Out damned spot! Out, I say Here’s the smell of the blood still, All the perfumes of Arabia will not Sweeten this little hand. Oh, Oh, Oh!” —William Shakespeare’s Lady Macbeth, in Macbeth

  2. Unknown Stain at a Scene Questions to be answered: • Is it blood? • Is it human blood? • Whose is it? • Determine blood type, alcohol content, drugs present • Determine the method(s) in which blood may have been deposited

  3. Blood Evidence • Class evidence for blood = blood type. • DNA = individual evidence. • Blood stain patterns are considered circumstantial evidence in a court room. Experts argue many points including direction of travel, height of the perpetrator, position of the victim, left/right hand, whether the body was moved, etc.

  4. Blood Spatter Evidence Deals with: • Physical properties of blood • Patterns produced under different conditions as a result of various forces being applied to the blood.

  5. Serology Examination and analysis of body fluids. • Saliva, semen, urine, and blood. • Limited funds/time required for DNA testing - most labs still use many of the basic serology testing procedures.

  6. Human vs Non-Human Blood • Microscopic observation – we will do this  • Precipitin test (Very sensitive; requires only a small amount of blood). - blood injected into a rabbit - antibodies are formed - rabbit’s blood is extracted as an antiserum and antiserum is placed on sample blood. - sample will react with human proteins if human blood is present.

  7. Blood Characteristics • Plasma is the fluid portion of the blood (55%) • Cells (45%) • Erythrocytes are red blood cells. They are responsible for oxygen distribution. • Leukocytes are the white blood cells; they are responsible for “cleaning” the system of foreign invaders. • Thrombocytes or platelets are responsible for blood clotting • Serum is the liquid that separates from the blood when a clot is formed.

  8. Non-Human Blood Larger nucleic red blood cells Frog Blood Kendall/Hunt Publishing Company

  9. Human Blood • Red blood cells are most numerous • White blood cells are larger and less numerous • Platelets are tiny, cellular fragments

  10. Human vs Non-Human Blood Microscopy Sketch the following: • One (1) HUMAN blood slide • Three (3) NON-human blood slides (there are many to choose from) • Bullet differences • Note “what it looks like to you” (camel, bovine, cat, dog, reptile, fish, frog, sheep, bird, limulus)

  11. Blood Droplet Characteristics • A blood droplet remains spherical in space until it collides with a surface • Once a blood droplet impacts a surface, a bloodstain is formed • A droplet falling from the same height, hitting the same surface at the same angle, will produce a stain with the same basic shape • Circumstantial evidence??? How will the shape change as the height is increased or decreased?

  12. Conditions Affecting Shape of Blood Droplet • Size of the droplet • Angle of impact • Velocity at which the blood droplet left its origin • Height • Texture of the target surface • On clean glass or plastic (nonabsorbent)—droplet will have smooth outside edges • On a rough surface (absorbent)—will produce scalloping on the edges

  13. Bloodstain Patterns • The harder, less porous surface, the more spatter will occur. • The pointed end of the blood stain faces the direction of travel. • A more prominent tail is visible.

  14. Bloodstain Patterns • The softer and more porous the surface, the more a blood drop will absorb into surface.

  15. Bloodstain Geometry - Lab #1

  16. Bloodstain Geometry - Lab #1 • Use dropper to drop blood on each of the different surfaces • Each surface should be repeated a total of 4 times (1”, 2”, 36”, and 72”) • Clean lab area after each surface • Whiteboards should be cleaned with cleaner • Record data, SKETCH, and analysis questions in Lab Notebook

  17. Questions Answered by Blood Spatter Interpretation • Distance between target surface and origin of blood • Point(s) of origin of blood • Movement and direction of person or object • Number of blows, shots, etc. causing bloodshed and/or the dispersal of blood. • Type and direction of impact that produced the bloodshed • Position of victim and/or object during bloodshed • Movement of victim and/or object after bloodshed

  18. Blood Impact Angle of impact—angle at which blood strikes a target surface. • The more acute aoi = more elongated the stain. • 90º angles = perfectly round drops • 80º angles -> more elliptical shape. • ~ 30º stain begins to produce a tail. • The more acute the angle, the easier it is to determine the direction of travel.

  19. Kendall/Hunt Publishing Company

  20. Bloodstain Patterns The shape of a blood drop: • Round—if it falls straight down at a 90º angle. • Elliptical—blood droplets elongate as the angle decreases from 90º to 0º; the angle can be determined by the following formula:

  21. Angle of Impact – Lab #2 Standardized/Theoretical Values *As the SURFACE angle increases, the Angle of IMPACT decreases*

  22. Area of Intersectionand Convergence Source can be determined by drawing lines from the various blood droplets to the point where they intersect. Area of convergence is the point of origin = the spot where the “blow” occurred. May be established at the scene with measurement of angles by use of strings or lasers.

  23. Bloodstain Terminology • Directionality—relates to the direction a drop of blood traveled from its point of origin • Terminal velocity—greatest speed a free falling drop of blood can accelerate in air. Dependent on acceleration of gravity and friction of the air against the blood—approximately 25.1 feet/second. • High velocity—greater than 25 feet per second, usually 100 feet per second; gives a fine mist appearance -> gunshot • Medium velocity—5 to 25 feet per second • Low velocity—5 feet per second or less

  24. Angular Impact by Horizontal MotionBlood Lab #3 • Measure 10 ft on floor • Mark “Start” and “Finish” lines • Use phone/watch for timing • Begin moving a couple of feet BEFORE • “Start” line and end a couple of feet AFTER • Measure length and width of spatter after EACH round • Sketch pattern or cluster of stains

  25. Bloodstain Terminology • Contact stain—bloodstains caused by contact between a wet blood-bearing surface and a second surface which may or may not have blood on it • Transfer—an image is recognizable and may be identifiable with a particular object • Swipe—wet blood is transferred to a surface which did not have blood on it • Wipe—a non-blood bearing object moves through a wet bloodstain, altering the appearance of the original stain

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