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3/20/14Thursday

3/20/14Thursday. AIM: How do forensic scientists determine the direction of blood spatter? Do Now: 1-Which blood type is the universal donor and WHY? BE specific 2- How is human blood typing useful to a CSI?

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3/20/14Thursday

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  1. 3/20/14Thursday • AIM: How do forensic scientists determine the direction of blood spatter? • Do Now: 1-Which blood type is the universal donor and WHY? BE specific • 2- How is human blood typing useful to a CSI? • Homework: Text read pages 317-318 TheSam Sheppard case.Answer the following questions: 1- What is the crime? • 2- Who are the victims? Suspects? • 3-What were Marilyn’s wounds? • 4- Why did Paul Kirk say Sheppard was NOT the killer?

  2. Rh factor: rheusus factor • Separate gene • If you have it you are Rh + and you make the protein • If you don’t have it you are Rh – and you don’t make the protein • 85% of humans are Rh positive • If a mother is Rh- and baby is Rh + the mother may produce the antibodies against the Rh factor and attack baby blood

  3. What is Blood?

  4. Introduction to Blood

  5. Identifying blood at a crime scene • High intensity light beams • Luminol • Flourescin • Both react with the iron part of hemoglobin to glow in the presence of blood

  6. Tuesday 3/25/14 • AIM: What information can be extracted from blood droplets? • DO NOW: 2 minute mystery: Murdered wife • HOMEWORK: Sam Sheppard case and questions

  7. What determines human blood type? Genes: code for the antigen protein on the surface of the RBC

  8. A blood sample is found at a crime scene. How would you determine if it is human or animal?

  9. Determining the source of a blood sample • Precipitant test • Must have fresh blood sample • Use animal serum (liquid that separates from clotted blood) which contains antibodies • Specifically antibodies against human antigen • If it agglutinates or clumps you have human blood • Hemastix:turn color in the presence of human hemoglobin • Can work on dried blood • Changes from yellow to green if blood is present

  10. Human Blood Testing- Presumptive Tests - YouTube

  11. Blood Spatter (or splatter) Blood drops form different shapes and sizes Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

  12. Information gotten from blood spatter analysis • Location of assailant • Height of assailant • How many times they swung or struck the victim • Right or left handed • Location of victim • How far were they from the victim • How fast the impact was • How much force was exerted

  13. Pd 9 tuesday

  14. Tuesday 3/25/14 • AIM: What information can we gather from blood spatter analysis? • DO NOW: 1- Is blood analysis considered circumstantial or individual evidence? EXPLAIN 2-List some factors that can effect the size and shape of a blood droplet • HW: Sam Sheppard case

  15. Homework: Text read pages 317-318 TheSam Sheppard case.Answer the following questions: 1- What is the crime? • 2- Who are the victims? Suspects? • 3-What were Marilyn’s wounds? • 4- Why did Paul Kirk say Sheppard was NOT the killer?

  16. Blood spatter shape is effected by • volume of droplet • Angle of impact • force • Velocity • Height • Surface texture • Smooth surfaces = smooth edges • Rough surfaces= rough edges

  17. Human blood type percentage • O=43% • A = 42% • B = 12% • AB = 3%

  18. Science of Murder: Blood Spatter - YouTube

  19. Determining Distance Blood Falls Blood drops fall as small spheres

  20. Blood Spatter > Distance Determining Distance Blood Falls • Drops form circle when hitting surface • Size depends on speed of blood drop and type of surface it hits

  21. Blood Spatter > Distance Determining Distance Blood Falls Faster drop = larger diameter (size) Higher distance = larger diameter Due to air resistance, speed maxes out at distances above about 7 feet

  22. Blood Spatter > Distance Determining Distance Blood Falls However, size of drop also depends on the volume of the drop. Volume depends on the object blood originated from (needle = small; bat = large).

  23. Blood Spatter > Distance Determining Distance Blood Falls Since the volume of blood is unknown… The distance a drop has fallen cannot be measured.

  24. Blood Spatter Effect of Surface • Smooth surface = smooth sphere • Rough surface may cause some splatter

  25. Surface • The harder and less porous the surfae the less the blood will break apart • On softer surfaces the blood breaks apart

  26. How can you determine the direction of blood?

  27. Directionality: the direction a droplet of blood travels in space from its point of origin Determining Direction of Blood Narrow end of a blood drop will point in the direction of travel.

  28. Shape of blood droplet Round 90 degree angle Elliptical 0-90 degrees

  29. Angle of impact • The more acute the angle of impact, the more elongated the stain • At about 30 degrees the drop will begin forming a tail

  30. Blood Spatter > Direction Determining Direction of Blood If more than one drop (from spatter) results, the point of origin can be determined

  31. Area of convergence • The spot where the blow occurred • Can be established by the measurement of angles and drawing lines from each droplet to their meeting point

  32. Blood Spatter > Direction Determining Direction of Blood If more than one drop (from spatter) results, the point of origin can be determined

  33. Blood Spatter > Direction Determining Direction of Blood This is a 2-dimensional point of origin. It is possible to determine the 3-D point of origin

  34. Determining Direction of Blood • The angle can be determined mathematically. • Width/Length, then take the inverse sin (sin-1). • This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle) • Impact angle: angle at which the blood droplet hits the surface

  35. Wednesday 3/26/14

  36. Blood Spatter > Direction • For each blood drop, a string can be guided back to the point of origin.

  37. How does velocity effect blood stain pattern • Terminal velocity: greatest speed a free falling blood droplet can accelerate • 25.1 feet per sec • High velocity <25 feet/sec usually about 100 ft/sec • Gives a fine spray mist • Size of individual blood drops are less than 1 mm • Medium velocity: 5 to 25 ft/sec • Size of individual drop is greater than 1 mm • Low velocity: 5 ft/sec or less

  38. Blood Spatter Types of Spatter • Spattered Blood = random distribution of bloodstains that vary in size • Amount of blood and amount of force affect the size of blood spatter. • Can result from gunshot, stabbing, beating

  39. Blood Spatter Spattered Blood can: • Help determine the location of the origin of the blood source. • Help determine the mechanism which created the pattern.

  40. Blood Spatter Spattered Blood In general, for higher impacts, the pattern is more spread out and the individual stains are smaller. Low impact = beating High impact = gunshot

  41. Blood Spatter Types of Spatter Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot. • Not all gunshots will result in misting. • If misting is present, it is most likely a gunshot.

  42. Blood Spatter Gunshot Spatter Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).

  43. Blood Spatter Types of Spatter Beating and Stabbing Spatter = larger individual stains First blow usually doesn’t result in spatter since there is not yet any exposed blood.

  44. Blood Spatter Types of Spatter Satellite Spatter = free falling drops of blood that fall onto a spatter pattern. • These drips are usually much larger than impact spatter. • However, blood dripping into blood can create a spatter.

  45. Blood Spatter Types of Spatter Castoff Pattern = Blood flung off of swinging object. Can reconstruct where assailant and victim were positioned.

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