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Unit 2: Physical Evidence Fingerprinting, Ballistics, & Blood Spatter

Unit 2: Physical Evidence Fingerprinting, Ballistics, & Blood Spatter. 1. History of Fingerprints. Pgs. 60-62. History of Fingerprints: Cont’d. Pgs. 60-62. Summary of Will West Case Study. Pgs. 61-62. Types of Fingerprints. Develop 6-13 weeks during fetal development.

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Unit 2: Physical Evidence Fingerprinting, Ballistics, & Blood Spatter

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  1. Unit 2: Physical EvidenceFingerprinting, Ballistics, & Blood Spatter

  2. 1. History of Fingerprints Pgs. 60-62

  3. History of Fingerprints: Cont’d Pgs. 60-62

  4. Summary of Will West Case Study Pgs. 61-62

  5. Types of Fingerprints Develop 6-13 weeks during fetal development • Whorl- core closed in center • ~ 20% of people have these Ridge Core

  6. Types of Fingerprints Loop- one or more ridges entering one side, curve, then leave from the same side it entered ~65% population has loop Core Ulnar Loop- Loop extends toward pinky Radial Loop- loop extends toward thumb Left hand

  7. Types of Fingerprints Arch- ridges enter one side and exit on the opposite side while rising in the middle Plain Arch Tented Arch

  8. Fingerprint Ridge Classification: Minutiae Pg. 57

  9. Types of Fingerprints Lifted from Crime Scene • Visible- see them • Blood, chalk, grease • Plastic • Impressions, wax, soap • Latent- cannot see • Caused by perspiration, powders, fuming • Visualizing latent prints • Dusting • Hard, non-absorbent surfaces • Different colored powders • Fuming • Nonporous surfaces, super glue • Lasers

  10. Fingerprinting • AFIS- automated fingerprint ID system • FBI- keeps and maintains files • Search time- immediate • Matching and legal considerations

  11. Firearms & Ballistics • Why are guns/bullets so important to know about in forensics?

  12. Firearms & Ballistics Forensic Firearm Examiners Analyze: • Guns, Bullets and Shell Casings • Class Evidence: Determine what kind of gun firedthe bullet • Individual Evidence: Match bullet or shell casing to • A specific weapon • A sample from a different crime scene to link the two • Ballistics (how bullets behave after being fired) • Estimate • Distance between gun muzzle and victim • Trajectory of bullets Parabolic Motion

  13. Gun Anatomy & Terminology 3. 1. Muzzle: 2. Barrel: 3. Safety: 4. Hammer: 5. Trigger: 6. Magazine: 7. Bore: 8. Land: 9. Groove: Rifling Twist: clockwise or counterclockwise Caliber: Butt stock: 4. 1. 2. 5. 6. 12. 7. 8. 9.

  14. Ammunition Bullet caliber: diameter of bullet

  15. How a Gun Works Breech: attached to action • Overall: Burn fuel, creates gas pressure, projectile launches • Load ammunition • Pull trigger • Hammer hits cartridge case • Primer ignites, sets off gun powder • Bullet forced forward through grooved barrel spin Longer barrel: from gas pressure- more accurate, travel farther

  16. Class Characteristics: Match Bullet to Type of Gun • Manufacture • Winchester • Shape • Rimless, rimmed • Caliber • Diameter of bullet • Composition • Brass, steel, plastic

  17. Individual Characteristics: Matching a Bullet to a Specific Gun • Striations : Markings on a bullet created by the lands and grooves (rifling) in the barrel as the bullet travels out • No rifling is exactly the same from one gun to the next (like a fingerprint) A B

  18. Individual Characteristics: Matching a Bullet to a Specific Gun • Breech marks- marks left on back of cartridge casing • As bullet moves forward, casing moves backward against breech making an impression

  19. Individual Characteristics: Matching Bullets to a Specific Gun • Firing pin marks • Marks created by the firing pin as it strikes the bottom of the cartridge when shot • Extractor & ejector marks • Marks left when bullet casing released after gun fired

  20. Residue from Guns • Gunpowder thrown backward and forward • Infrared photography reveals residue patterns • Can determine how far away a shot was fired from • Halo of soot around hole = 12-18” away • Halo with specks = 18-25” away • Only specks = 26 +” away

  21. Examination & Use in Court • Use of comparison microscope • No rules on number of points of comparison • FBI maintains records of class characteristics of all weapons: IBIS

  22. Blood Spatter • Patterns left by spatter • Projected, or smeared blood can help interpret & reconstruct crimes • Direction of Travel • Tail points in direction of travel • Angle of Impact • Angle of impact (i) = Arc sin (w/l) • Can be used to determine victim’s position

  23. Blood Spatter: Cont’d • Position of Origin • Tracing pattern back to source/area of convergence • Blood Droplet Speed Before Impact

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