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 Agenda

• DSL

• Hair and Fiber analysis notes

• Worksheet – Due Friday 1/16

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

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 texture can vary considerably

depending upon the ratio of cuticle to

medulla

How a hair grows

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

Appearance of different hair (or

fur) types will vary from

animal to animal

Cat hair

Dog hair

Rabbit hair

Other animal hair

Deer Muskrat

• Deer – no cortex, medulla filled with spheres

• Mouse – parallel rows of beads

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?

Caucasoid

Oriental

Negroid

Hair from different races

Negroid Mongoloid Caucasoid

Hair cannot be absolutely identified as to race. Traits

associated are often and characteristics of races are

less distinct.

Some Caucasoid natural colors

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

Normal hair

Damaged hair

Burned Split ends Razor cut

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

DNA Analysis

• Only possible if ‘bulb’ at the base of the hair is intact

Bulb

Forcibly removed

Follicle intact Pulled

A BaselineUp to 50 hairs from each body region (head, pubic area, facial hair, etc., are needed to provide a baseline for comparability

Pubic hair

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

Natual vs. Synthetic

Cotton Rayon

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 .