forensics dsl didn't wilbur make a lovely chocolate cake last week? answer: burma. didn't...
TRANSCRIPT
Forensics DSL
• Didn't Wilbur make a lovely chocolate cake last week?
• Answer: Burma.
• Didn't Wilbur make a lovely chocolate cake last week?
Forensics Objectives
• I can explain the methods used to examine fibers in forensic science.
• I can describe why fiber analysis is important in the realm of forensic science.
Hair & Fiber Analysis
• Can be used to match a suspect with a crime scene
• Can be microscopically analyzed for similarity
• Comparisons continue to improve as forensic techniques improve
Part 1 Hair Background• Grows from a collection of cells
called a follicle
• The hair shaft is composed of three parts:
1. cuticle – outside covering of hair
shaft, can look like overlapping
roof shingles
2. Cortex – inside the cuticle, a pigmented layer
3. Medulla – runs down the center of the hair
shaft
Many photos can be obtained from hair dressing publications.
Many of the following are from this publication.
Hair fibers are excellent for ID study because:
• They resist decomposition
• May indicate drug use or poisoning
To distinguish between animal and human hair use a Medullary Index
diameter of hair’s medulla
Medullary Index =-------------------------------
diameter of the hair
M.I. = <.33 hair is human
M.I. =>.5 or more, hair is animal
Human Medullary Patternshas three types:
• Continuous medullary canal• Interrupted medulla
(regular interruption)• Fragmented medulla
(interruption irregular)
Hair Photos
• Can you identify the type of medullary pattern- continuous, interrupted and fragmented?
Hair cannot be absolutely identified as to race. Traits
associated are often and characteristics of races are
less distinct.
Additional Information
• Individuals of Oriental origin usually have a continuous medulla
• Dyed hair shows color distributed in cortex and medulla
• Bleached hair has a yellowish tint• As hair grows, natural color returns
Hair is ‘class evidence’ not individual evidence
What’s the difference?Varies in texture from one region of the
body to anotherRound or oval in cross-section in
CaucasiansOval or flat in cross-section in African
Americans
A BaselineUp to 50 hairs from each body region (head, pubic area, facial hair, etc., are needed to provide a baseline for comparability
Hair Comparison- Error rates(study done by FBI)
• Hair evidence (1996-2000) was DNA tested & microscopic examination 11% of hairs that were “matches” by examiners via microscopes were actually non-matches according to DNA. Conclusion: Microscopic matches are presumptive in nature and must be confirmed by DNA.
Central Park Jogger Case
5 teens convicted of brutally beating & raping “Central Park Jogger” (1989) Evidence: confessions by teens & hair on one defendant that “resembled” victim. Another man came forward & confessed to crime & had matching DNA (2002)
Fiber Analysis• Are considered class evidence (they are very
hard to individualize) Have probative value (can prove something) common at a crime scene Analyzed based on physical & chemical properties
Types of Fibers
Natural
• Silk
• Cotton
• Wool
• Cashmere (goats)
Synthetic• had to learn how to chemically
manufacture polymers first)
• Rayon (1911)• Nylon (1939)• Acetate• Acrylic• Spandex• Polyester
Individual vs. Class Evidence
Individual Evidence
• Really high probability of being linked to one, unique source
• Ex: Fingerprints, DNA, Bullets, Tire/ footwear patterns, Tool marks, Broken glass
Class Evidence• Object has characteristic
common to a group of similar objects
• Ex: Hair, Fibers, Blue jeans• Can increase the probability
of class evidence by finding things that can make it unique:
• Ex: stains, wear patterns on jeans
Probability & Class Evidence• Product Rule- Used to determine the probability of
finding a particular characteristic in a population.• Uses probability of each individually occurring and then
multiply them together, you can determine the chances of all the characteristics occurring at one time.
• Increases the probative value of the class evidence.• Ex: suspect seen wearing a white tshirt, jeans, and white
tennis shoes.
Product Rule Example:• Ex: Suspect seen leaving student parking lot where
window was broken & ipod stolen. Witness says suspect had: brown hair, wearing white shirt, and jeans. (assume: 1400 students)
• Brown hair = 70% of students have• white fibers = 10 % student have on• denim fiber= 20% students wearing• How many people should be called in?• (.7)(.1)(.2) = 0.014 or 1.4% of students will be wearing
this combination of items.• Roughly 20 students/1400 .