IST 224 One Week of Notes
IST 224 One Week of Notes IST 224
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This 10 page Class Notes was uploaded by Meghan Spielvogel on Monday February 15, 2016. The Class Notes belongs to IST 224 at Marshall University taught by Professor Shank in Fall 2015. Since its upload, it has received 34 views. For similar materials see Introduction to Forensics in Science at Marshall University.
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Clutch. So clutch. Thank you sooo much Meghan!!! Thanks so much for your help! Needed it bad lol
-Mr. Kelton Bartell
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Date Created: 02/15/16
Blood Stain Pattern Analysis 1. Bloodstain pattern a. A grouping or distribution of bloodstains that indicates through regular or repetitive form, order, or arrangement the manner in which the pattern was deposited. 2. Blood stain pattern analysis a. Blood stain pattern analysis can provide insight into i. Distance from the source of the blood to the pattern ii. Direction from which the blood impacted iii. Speed the droplet was traveling iv. Location of the point of origin v. Movement of a bleeding individual throughout the scene b. These conclusions may support or perjure statements made by witnesses, victims or suspects 3. Blood stain evidence a. In violent crimes, bloodstained evidence is useful for DNA, but can help investigators reconstruct events in a crime. b. A bloodstain is a deposit of blood on a surface (wall, floor, clothing, etc.). 4. Biological properties of blood a. Blood is a liquid tissue b. Blood delivers nutrients and oxygen to the cells and transports waste products away from cells. c. Red blood cells carry oxygen and carbon dioxide. d. white blood cells fights off infection and rejects foreign tissue. e. Platelets assist in clotting 5. Blood clotting a. In response to a wound, blood forms a clot, a gelatinous mass formed by a complex mechanism involving red blood cells, fibrinogen, platelets, and other clotting factors. b. Normally, blood clots in 315 minutes c. Blood clotting can be delayed i. Liver disease, genetic diseases like hemophilia ii. Medications like aspirin, warfarin iii. Vitamin K deficiency d. The heart pumps blood within a closed system, creating blood pressure. e. When a traumatic wound occurs to an artery, blood exits the wound in spurts with each beat of the heart, rather than in a steady flow. f. Blood can leave the body very rapidly from an arterial wound, before clotting can occur. g. Arterial blood is a bright red. h. Venous wounding causes steady blood loss, although it can be quite substantial with a large wound. Venous blood is quite dark red. i. Capillary bleeding usually occurs in superficial wounds, such as abrasions. 6. Biological properties of blood a. After wounding, blood pressure drops with excessive blood loss and the bleeding rate slows due to this lower pressure difference. b. Upon death, blood pressure falls to zero and bleeding stops. c. Death occurs due to lack of oxygen in the organs. 7. Wound types a. Incision: clean edges b. Laceration: jagged edges, possibly caused by serrated edge or a blunt object c. Puncture: penetrating straight wound, internal injuries d. Gunshot: tissue disruption caused by a projectile e. Abrasion: shallow wound skin injury f. Contusion (bruise): subdermal bleeding g. Different types of wounds leave characteristics blood patterns, based on the physical and biological properties of blood. h. A large amount of blood from a small wound means that the victim survived for a length of time. 8. Physical properties of blood a. Blood is a suspension of solids and gases in a liquid. b. Blood leaves the body as a liquid the follows the laws of motion and gravity c. Physical properties i. Blood is 6 times more viscous than water ii. Viscosity provides resistance to change in form or flow, causing blood to move slowly than water iii. Blood normally has a specific gravity of ~1.060, heavier than water iv. Surface tension of blood is less then water 9. Surface tension a. Gravity acts on blood as it exits the body b. Blood cohesion acts to reduce surface area by forming a sphere c. Smallest surface area to volume ratio is offered by a sphere d. A blood sphere is resist to penetration 10. Dripping blood a. Blood trickles downwards b. Blood drop grows until weight > surface tension c. Single drop breaks free (teardrop shape) d. Surface tension pulls in vertically e. And horizontally f. Shape forms a sphere (0.05 ml) g. Drop does not break up until impact 11. Drop sizes a. The standard drop size is about 0.05mL b. Rapid bleeding results in slightly larger drop c. Shaking movement casts off smaller drops. d. Gunshot wounds produce high velocity spatter that results in a spray of very tiny drops 12. Free falling blood droplets a. Blood droplet size affects both the terminal velocity and the distance that the droplet will fall before reaching terminal velocity. b. The highest from which a droplet falls affects the diameter of its spatter. c. A smooth surface will cause d. An irregular surface will the spatter to spread out create a broken edge and smoothly smaller spatter. e. 13. Wave castoff a. When a droplet bounces off a surface the tails of the parent and wave castoff will point toward each other. 14. Determining directionality a. Directionality is the characteristic of a bloodstain that indicates the direction blood was moving at the time of deposition b. The pointed end of a bloodstain always faces its direction of travel c. The impact angle can be determined by measuring the length and width of the ellipse formed d. At right angles the blood drop is circular 15. Angle of impact a. The bottom of the spatter stain will be more dense than the top of the stain 16. Physical properties of blood a. Blood forms a spherical projectile as it moves through the air, not as a teardrop b. The sphere of blood does not break up until impact with a solid surface c. The spherical shape of blood in flight is important for the calculation of the angle of impact of blood spatter when it hits a surface d. The angle is used to determine the point from which the blood originated (point of origin or more accurately, area of origin) 17. Area of convergence (2D area) a. To determine the area of convergence, investigators calculate the direction and angle of many blood stains b. For each blood stain analyzed, they place a string at the stain which is parallel to the angle of the blood droplet c. After many strings have been placed, a general area of convergence will appear where the strings overlap d. This can also be done on a computer with image analysis software 18. Trigonometry and angle of impact a. To determine the angle of impact i. Measure the width (smaller number) and length (bigger number) of the blood spatter. Length is longer than width. ii. Divide width by length iii. Take the arcsine of you result iv. This formula will not produce aocurate results at o extreme angles (less than 10 or greater then 60 ) 19. Point of origin (3D volume) a. The procedure for generating the point of origin is just like the area of convergence, except for the angle of impact for each stain is calculated b. This is a method of adding a third dimension to the 2D area of convergence calculation c. This is a method of adding a third dimension to the 2D area of convergence calculation d. The procedure for generating the point of origin is just like the area of convergence, except the angle of impact for each stain is calculated. e. The term point of origin is really a misnomer, as the 3D intersection of the string creates a 3Dvolume rather than a single point f. This can also be done with a computer by taking careful measurements at the scene for each blood droplet’s dimensions, location, and direction. 20. Limitations of the model a. Projectiles launched at an angle do not follow a straight line b. The point of origin is actually lower than calculated because the blood follows an arc rather than a line, taking gravity into account c. At high velocities (gun shots) the linear model projectile motion is fairly accurate d. This model is better suited to disproving testimony than to accurately re constructing the events at a crime scene. e. f. g. h. i. j. k. l. m. n. o. 21. Size of spatter reflects velocity a. Low velocity (5 f/s, 1.5m/s) i. e.g. free falling drops, cast off from weapon b. medium velocity (25100f/s, 7.530 m/s) i. e.g. baseball bat blows c. high velocity (>100 f/s, 30 m/s) i. e.g. gunshot, machinery 22. low velocity blood spatter a. blood source subjected to LV i. < 5f/s (1.5 m/s) b. Spot diameter: mostly 48 mm i. Some smaller, some larger c. Free falling drops (gravity only) d. Cast off from fist, shoe, and weapon e. Dripping f. Splashing g. Arterial spurting 23. Medium velocity blood spatter a. Blood source subjected to medium velocity impact i. 25100 f/s, 7.530m/s b. Spot diameter: mostly 14mm c. Blows with weapon (e.g. baseball bat) 24. Blood castoff from weapon a. First blow causes bleeding b. Subsequent blows contaminate weapon with blood c. Blood is castoff tangentially to arc of upswing or backswing d. Pattern and intensity depends on i. Type of weapon ii. Amount of blood adhering to weapon iii. Length of arc 25. Castoff pattern a. A bloodstain pattern resulting from blood drops released from an object due to its motion 26. High velocity blood spatter a. Blood source subjected to high velocity impact i. >100 f/s, 30 m/s b. Fine mist: spot size <0.1 mm c. Small mass limits spread to 1 meter d. Some larger droplets can reach further e. Gunshot i. Backspatter from entry wound ii. Forward spatter from exit wound f. High speed machinery can also have high velocity spatter 27. Gun shot back spatter a. Arises from entrance wound b. Passes back towards weapon and shooter c. Seen only at close range of fire d. Seen on i. Inside of barrel ii. Exterior or weapon iii. Hand, arm, chest of shooter 28. Void patterns a. An absence of blood in an otherwise continuous bloodstain or bloodstain pattern b. The blank space on the surface or object may give a clue as to the size and shape of the missing object or person 29. Wipe pattern a. Object moves though a wet bloodstain b. Feathered edge suggests direction c. Often a wipe is an attempt to clean up an area 30. Flow patterns a. Results from the movement of a volume of blood on a surface due to gravity or movement of the target b. Blood flows horizontally and vertically c. Altered by containers, obstacles d. Often ends in blood pool 31. Transfer stain a. A bloodstain resulting from contact between a bloodbearing surface and another surface b. Transfer from i. Hand/ fingers ii. Shoes/ weapons iii. Hair c. Transfer to i. Wall/ ceilings ii. Clothing/ bedding d. Produces mirrorimage of bloodied object 32. Drip trail a. A drip trail is a series of blood drops that are separate from other patterns, formed by blood dripping off an object or injury. b. The stains form a kind of line or path usually made by the suspect after injuring or killing the victim or injuring themselves. c. The pattern may show movement, lead to a discarded weapon, or provide identification of the suspect by his or her own blood. d. The shape of the stains in trail pattern can help investigators determine the direction and speed at which a person was moving. 33. OJ Simpson Murder Trial a. June 12, 1994: Nicole Brown Simpson and Ronald Goldman are stabbed to death. Their bodies found in the front courtyard of the Nicole's condominium in Brentwood. b. Nicole Brown Simpson is the divorced wife of O J Simpson, a wellknown retired football star and actor. c. Goldman was a waiter who had served dinner to Nicole and her family that evening and was returning her mother’s glasses in an envelope. d. Next day, O J Simpson returns from Chicago and brought in for questioning. e. f. g. 34. Documenting bloodstain evidence a. Investigators should note, study, and photograph each pattern and drop to accurately record the location of specific patterns and to distinguish the stains from which laboratory samples were taken. b. In many crime scenes, the investigator uses lasers or 3D photography instead of string to allow others access to the crime scene. c. Document bloodstain patterns in photographs i. The grid method involves setting up a grid of squares of known dimensions over the entire pattern. ii. The perimeter ruler method involves setting up a rectangular border of rulers around the pattern and then placing a small ruler next to each stain. 35. SWGSTAIN a. FBI Scientific Working Group on Bloodstain Pattern Analysis b. The mission of SWGSTAIN is to promote and enhance the development of quality forensic bloodstain pattern analysis (BPA) practices through the collaborative efforts of government forensic laboratories, law enforcement, private industry, and academia. c.
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