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BU ANTH 245 - The Nature of Forensic Evidence Part 2

Course: Anth 245-
Type: Lecture Note
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Anthro 245 1st Edition Lecture 6 Outline of Last Lecture I. The Nature of Forensic Evidence Part 1Outline of Current Lecture II. The scientific method applied III. Analytical tools IV. Class characteristics and individual characteristicsV. Matching and probabilityVI. Forensic databasesVII. SamplesCurrent LectureII. Scientific method applied: • Observe evidence left at the scene or of the victim or suspect ◦ E.g. body with a gunshot wound • Create a question ◦ Was the bullet in the victim fired from the suspect's gun? • Create a hypothesis ◦ The bullet in the victim is a match to the suspect's gun • Test the hypothesis - comparative method ◦ E.g. compare striation on bullets\ • Evaluate/analyze data ◦ E.g. striation patterns are different • Interpret the results - inclusion, exclusion, or inconclusive ◦ The victim was not shot with the suspect's gun III. Analytical tools • Light microscope ◦ Soil, fibers, glass • Comparison microscope ◦ Look at two things side by side These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.◦ Some of these may also transmit light ◦ Used for things such as bullets, fibers, and hairs • Scanning electron microscope (SEM) ◦ Finite detail of an object's surface ◦ E.g. comparison of cut marks by a suspect's knife IV. Class characteristics • Properties of evidence only associated with a group and not a single source • For example, certain tool marks or paint chips • Problem of lack of probabilities ◦ E.g. probability that a particular fiber came from this one particular sweater? ◦ More likely to find evidence with group characteristics than individual characteristics • Characteristics associated with a group, but not a single source ◦ Bullet is .45 caliber, not .22 caliber ◦ Hair is human, not dog ◦ Tire tread is Goodyear, not Firestone ◦ White powder is cocaine, not sugar Individual characteristics • Flaws, unique traits that make one object different from all similar objects ◦ E.g. nick on a blade that make unique cut mark, or the wear on a tire • Positive identification requires one or more individual characteristics Limitations and cautions • When is the line crossed between class characteristics and individual ones? ◦ E.g. color layers on a paint chip ◦ E.g. features in fingerprints • Look at quality, and experience of examinerIdentification vs. comparison • Identification - determining substance's physical or chemical identity ◦ -E.g. suspects from a blood sample • Comparison - ascertaining whether two or more objects have common origins ◦ E.g. fibers on clothes compared to fibers in a car Individualization • Demonstrates the uniqueness of some item of evidence • Principle that no two things are exactly the same ◦ Example: no two objects break in the same way ◦ No two tires wear in the same way ◦ No two condom wrappers tear in the same way V. Matching • How many points of similarity are required for individualization? ◦ No hard, fast rules ◦ Depends on quality of sample and experience of the examiner ◦ Cannot have inconsistencies • Have to make probability statements based on the population at large Probability • Evidence has little value if it is not rare/unique/specific • Define the odds at which a certain event will occur VI. Forensic databases • Fingerprints ◦ IAFIS and AFIS ▪ Integrated automated fingerprint identification system • DNA ◦ CODES▪ Combined DNA index system ◦ Forensic and offender indices ▪ Launched by the FBI • IBIS - Integrated ballistic identification system • PDQ - International forensic automotive paint data query VII. Samples • Exemplar samples Known samples ◦ Come from suspect (usually) ◦ Objects found away from the crime scene • Questioned samples ◦ Unknown - Comes from crime scene Possible outcomes • Questioned sample ◦ Inconsistency with exemplar sample (inclusion) ◦ Consistent with exemplar sample (exclusion)


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