Forensics DSL

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Forensics DSL

• Didn't Wilbur make a lovely chocolate cake last
  week?
• Answer Burma.
• Didn't Wilbur make a lovely chocolate cake last
  week?

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Forensics Agenda

• DSL
• Hair and Fiber analysis notes
• Worksheet Due Friday 1/16

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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.

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Hair Fiber Analysis
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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

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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

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• Cortex inside the cuticle, a pigmented layer
• Medulla runs down the center of the hair
• shaft

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Many photos can be obtained from hair dressing
publications. Many of the following are from this
publication.
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Hair texture can vary considerablydepending upon
the ratio of cuticle to medulla
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How a hair grows
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• Hair fibers are excellent for ID study because
• They resist decomposition
• May indicate drug use or poisoning

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To distinguish between animal and human hair use
a Medullary Index

• diameter of hairs medulla
• Medullary Index -------------------------------
• diameter of the hair
• M.I. lt.33 hair is human
• M.I. gt.5 or more, hair is animal

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Appearance of different hair (or fur) types will
vary from animal to animal
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Cat hair
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Dog hair
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Rabbit hair
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Other animal hair
Deer
Muskrat
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• Deer no cortex, medulla filled with spheres
• Mouse parallel rows of beads

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Human Medullary Patternshas three types

• Continuous medullary canal
• Interrupted medulla
• (regular interruption)
• Fragmented medulla
• (interruption irregular)

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Hair Photos

• Can you identify the type of medullary pattern-
  continuous, interrupted and fragmented?

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Caucasoid
Oriental
Negroid
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Hair from different races
Negroid
Mongoloid
Caucasoid
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Hair cannot be absolutely identified as to race.
Traits associated are often and characteristics
of races are less distinct.
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Some Caucasoid natural colors
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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

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Normal hair
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Damaged hair
Burned
Split ends
Razor cut
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Hair is class evidence not individual
evidence Whats 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
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DNA Analysis

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

Bulb
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Forcibly removed
Follicle intact
Pulled
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A Baseline

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

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Pubic hair
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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.

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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)
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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

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Types of Fibers

• Synthetic

• Natural

• had to learn how to chemically manufacture
  polymers first)
• Rayon (1911)
• Nylon (1939)
• Acetate
• Acrylic
• Spandex
• Polyester

• Silk
• Cotton
• Wool
• Cashmere (goats)

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Natual vs. Synthetic

• Cotton

• Rayon

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Individual vs. Class Evidence

• Individual Evidence

• 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

• Really high probability of being linked to one,
  unique source
• Ex Fingerprints, DNA, Bullets, Tire/ footwear
  patterns, Tool marks, Broken glass

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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.

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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 .