1. Trace Evidence

2. What is Trace Evidence?
Trace evidence: minute amounts of substances transferred by physical contact
Edmund Locard’s principle: “Every contact leaves a trace”
Common Forms of Trace Evidence:
Hair
Textile fibers
Paint and paint chips
Glass fragments
Bloodstains

3. Crime Scene Preservation and Evidence Collection
Must remember and be prepared to collect and catalog evidence correctly.
What is Chain of Custody?
A list of all persons who came into possession of an item of evidence.
What are things to be done?
What are things NOT to do?

4. Hair The study of hair is called: Tricology
Hair is made of Keratin, which is the primary component of finger and toe nails
Hair is produced from a structure called the hair follicle. (No follicles are made after birth)
Hair color comes from pigments, which are chemical compounds that reflect certain wavelengths of visible light
Hair shape and texture are influenced by genetics.
Hair physical appearance can be changed by nutrition and alterations.

5. Hair Identification Must determine Animal or Human
Must determine what part of the body
Must match or NOT match to another person
To do this we look at…

6. Hair Structure Hair is composed of three principal parts:
Cuticle – outer coating composed of overlapping scales
Cortex – protein-rich structure around the medulla that contains pigment
Medulla – central core (may be absent)
The structure of hair has been compared to that of a pencil with the medulla being the lead, the cortex being the wood and the cuticle being the paint on the outside.

7. Hair Structure Cuticle
The cuticle varies in:
Its scales,
How many there are per centimeter,
How much they overlap,
Their overall shape, and
How much they protrude from the surface
Its thickness
Whether or not it contains pigment.
Characteristics of the cuticle help determine difference is species but NOT in distinguishing different people.
Info: Image:

8. Cuticle Cont’d Cuticle has 3 Basic Patterns:
Coronal or Crown: scale pattern resembles a stack of crowns one on top of the other
Spinous or Petal-like: scale pattern in triangular shapes that protrude from the hair shaft
Imbricate: flattened-scale type that consists of overlapping scales with narrow margins

9. Hair Structure
Cortex
The cortex varies in:
Thickness
Texture
Color
Distribution of the cortex is perhaps the most important component in determining from which individual a human hair may have come. Microscopic examination can also reveal the condition and shape of the root and tip.
Info: Image:

10. Hair Structure Medulla The medulla may vary in: Thickness
Continuity - one continuous structure or broken into pieces
Opacity - how much light is able to pass through it
It may also be absent in some species.
Like the cuticle, the medulla can be important for distinguishing between hairs of different species, but CANNOT differentiate between hairs from different people.

11. Medulla Cont’d Medulla has 4 Patterns:
Absent: no medulla present (or visible)
Continuous: the medulla extends throughout the entire strand with no breaks
Interrupted: medulla has repetitious breaks in a consistent pattern
Fragmented: the medulla has breaks and separations that have no pattern

13. Medullary Index Human hair has an index of 1/3 or less
Animal hair has an index of ½ or more

14. Human & Animal Hair (continued)
Medulla
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15. Characteristics Pigment (melanin, but redheads have pheomelanin)
Colors – light, medium, dark; reddish-brown, brown, black, etc.
Sizes – fine, moderate, large
Density – light, moderate, heavy
Distribution – random, peripheral,
even, central, one-sided
Dyed Human Hair
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16. Roots
Postmortem Root Band (aka "Dead man's root”) a dark band that may appear near the root of a hair originating from a decomposing body
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17. Hair Analysis Day 1 Configuration (straight, wavy, curly)
Color/Pigment
Shaft diameter (thin, moderate, coarse)
Animal or Human?
Medulla Pattern

18. Human & Animal Hair 3 Main differences Human Hair Animal Hair Pigment
remains constant in its color and pigmentation throughout the length of the shaft
often exhibits rather rapid and radical color changes
Medulla
thin, taking up no more than 1/3 of the hair shaft diameter; amorphous
very wide; its structure is very regular and well-defined (with certain patterns)
Scale Structure
has overlapping imbricate (or flattened) scales with narrow margins
some have coronal (crown-shaped) scales or spinous (petal-shaped) scales
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19. Human & Animal Hair (continued)
Rabbit hair
Medulla
Medulla
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20. Scales Imbricate Scales Human Imbricate Scales Coronal Scales Diagram
Bat Hair
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21. More Examples Spinous Scales Diagram Mink hair Scales in Deer hair
Medulla in opossum hair
Scales in Deer hair
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22. Racial Comparison

23. Racial Origin Caucasian
moderate shaft diameter with very little variation
light to moderate pigment density with fairly even distribution
oval-shaped cross-section
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24. Racial Origin (continued)
Caucasian Head
Hair cross-section
Caucasian
Head hairs
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25. Racial Origin (continued)
Mongoloid
coarse shaft diameter
streaky pigments with heavy density
thick cuticle
round cross-section
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26. Racial Origin (continued)
Mongoloid Head Hairs
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27. Racial Origin (continued)
Negroid
fine to moderate shaft diameter
considerable variation throughout the hair shaft with prominent twists and curls
heavy pigment density with aggregate pigment clumpings
flat cross-section
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28. Racial Origin (continued)
Negroid head hairs
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29. Variations
Why do we need to examine each hair sample from root to tip?
Five Regions of a single head hair
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30. Variations (continued)
One person's
head hair
One person
of multiple race
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31. Somatic Origin
Hairs from different parts of the body exhibit different characteristics:
Head hairs
Typically much longer than other hairs on the body
Generally soft and most likely to have artificial treatment (bleaching, dyes)
Pubic hairs
Typically coarse in diameter with wide variations
Pronounced medulla
Buckling (diameter variation) occurs
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32. Somatic Origin (continued)
Limb hairs (arm or leg)
Fine diameter with little variation
Arc-like, gross appearance
Tips are usually tapered, often blunt and abraded, rounded scale ends due to wear
Soft texture
Facial hairs (beard/mustache)
Very coarse diameter with irregular or triangular cross-sections
Very broad and continuous medulla
Medulla may be double
Stiff texture
Beard hair
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33. You MUST know how to identify:
Determine Human or Animal
Root characteristics
Configuration (wavy, curly, straight)
Shaft diameter (thin, moderate, course)
Color
Pigment size and density
Pigment distribution
Medulla pattern (medullary index)
Cuticle pattern
Race (if human)
Somatic origin (if human)

34. Fibers

35. Fibers
A fiber is the smallest unit of a textile material that has a length many times greater than its diameter.
Fibers can occur naturally as plant and animal fibers, but they can also be man- made.
The type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers and the significance of fiber associations.

36. Fiber Evidence
Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. 
They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. 
For analysis, they are first determined to be natural, manufactured, or a mix of both.

37. Fiber Number and Analysis
The greater the number of fibers, the more likely that contact actually occurred between the victim and suspect
Cross transfers of fiber often occur in cases in which there is person-to-person contact
Investigators hope that a fiber is traceable back to the offender and can be found at the crime scene.
Success in solving crimes often hinge on the ability to narrow the sources for the type of fiber found.

38. Forensic Fiber Analysis
Why would this information be valuable to a forensic scientist?
The world produced approximately 80 billion pounds of fabric in 1995, about half of which was cotton
The other approximately 44 billion pounds of fiber were manufactured or synthetic.
Table 1. U.S. Annual Production for Manufactured Fibers: 1995 (millions of pounds)
Fiber
Product
Polyester
3,887
Nylon
270
Olefin
521
Rayon/Acetate/Triacetate
498
Acrylic/Modacrylic
432
(Table 1 [6]). All these fibers were used in a variety of applications including but not limited to clothing, household textiles, carpeting, and industrial textiles.
It could be argued that the large volume of fibers produced reduces the significance of a fiber association discovered in a criminal case. It can never be stated with certainty that a fiber originated from a particular textile because other textiles are produced using the same fiber types and color. The inability to positively associate a fiber to a particular textile to the exclusion of all others, however, does not mean that a fiber association is without value. Considering the volume of textiles produced worldwide each year, the number of textiles produced with any one fiber type and color is extremely small. The likelihood of two or more manufacturers exactly duplicating all of the aspects of the textile is extremely remote (see endnote 2). Beyond the comments made previously about color, shade tolerance differs between dyeing companies. Therefore, color may vary demonstrably from batch to batch. Also, the life span of a particular fabric must be considered. Only so much of a given fabric of a particular color and fiber type is produced, and it will eventually end up being destroyed or dumped in a landfill.

39. Fiber Evidence Downfall
The problem with fiber evidence is that fibers are not unique. 
Unlike fingerprints or DNA, they cannot pinpoint an offender in any definitive manner. 
There must be other factors involved

40. Natural Fibers vs Manufactured
Natural fibers come from plants (cotton) or animals (wool). 
Manufactured fibers are synthetics like rayon, acetate, and polyester, which are made from long chains of molecules called polymers. 

41. Natural Fibers
Cotton fibers are the plant fibers most commonly used in textile materials
Cotton fibers vary in: length and degree of twist which contributes to the diversity of these fibers.
Cotton fibers

42. Animal Fiber: Wool
Wool is the most frequently used in the production of textile materials
The most common wool fibers originate from sheep.
Finer wool fibers are used in the production of clothing coarser fibers are found in carpet.
Fiber diameter and degree of scale protrusion of the fibers are important characteristics.
Wool fibers

43. Other Animal Fibers
Although sheep's wool is most common, wool fibers from other animals including: camel, alpaca, cashmere, mohair, llamas, fur (rabbit, mink, beaver, and muskrat)
The identification of less common animal fibers at a crime scene or on the clothing of a suspect or victim would have increased significance.

44. Man-Made Fibers
More than half of all fibers used in the production of textile materials are man-made.
Some man-made fibers originate from natural materials such as cotton or wood and are classified as regenerated fibers (rayon, acetate, and triacetate); others originate from synthetic fibers (nylons, polyesters, and acrylics)
Polyester and nylon fibers are the most commonly encountered man- made fibers, followed by acrylics, rayon, and acetates.
The amount of production and use of a man-made fiber influence the rarity of a given fiber
Cross section of man-made fibers

45. Man-Made Fibers
The cross section of a man-made fiber can be manufacturer- specific
Some cross sections are more common than others, and some shapes may only be produced for a short period of time.
Unusual cross sections encountered through examination can add increased significance to a fiber association.
Cross-sectional views of nylon carpet fibers as seen with a scanning electron microscope (SEM)

46. Fiber Forensics
Generally, the analyst gets only a limited number of fibers to work with—sometimes only one.
Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home
Fibers are laid side by side for visual inspection through a microscope.

47. Important Considerations
If the victim is immobile, very little fiber loss will take place, whereas the suspect's clothing will lose transferred fibers quickly.
The likelihood of finding transferred fibers on the clothing of the suspect a day after the alleged contact may be small, depending on the subsequent use or handling of that clothing.

48. Steps of Fiber Analysis
The first step in fiber analysis is to compare color and diameter (shape and size)
Dyes can also be further analyzed with chromatography 
Chemical Composition
Microscopic evidences
Again Fiber evidence can only take you so far!!! There are no databases with easy mass comparison

49. Summary of Steps of Fiber Analysis
In short, the fiber analyst compares shape, dye content, size, chemical composition, and microscopic appearances, yet all of this is still about "class evidence.“
 Even if fibers from two separate places can be matched via comparison, that does not mean they derive from the same source, and there is no fiber database that provides a probability of origin.