1. FORENSIC SCIENCE Trace Evidence

2. Introduction
Trace Evidence--any small pieces of material, man-made or naturally occurring
Most common examples:
Hair
Fiber

3. Test Questions for Trace Evidence
What is it?
Is it man-made or natural?
What is its source?
How common is it?
Can it be identified to a single source?

4. Hair
Human hair is one of the most frequently found pieces of evidence at the scene of a violent crime. It can provide a link between the criminal and the act.
From hair one can determine:
Human or animal
Race
Origin
Manner in which hair was removed
Treated hair
Drugs ingested

5. DNA
The hair shaft contains abundant mitochondrial DNA--inherited only from our mothers. It can be typed by comparing relatives if no DNA from the body is available.
Only the root contains nuclear DNA.

6. Hair Morphology The Study of Structure and Form
Parts of the hair
Shaft--part of the hair that sticks out of the skin
Root--lies below the epidermis
Follicle--structure from which the hair grows

7. Hair Growth Terminology
Anagen--hair that is growing
Catagen--hair at rest
Telogen--hair that is dying
Length mm per day or 1 centimeter per month; approximately one half inch per month

8. Hair Cuticle
The cuticle is the outermost layer of hair which is covered with scales. Scales also always point toward the tip of the hair. These scales differ between species of animals and are names based on their appearance. Some of these scales are variations of the same and include:
Mosaic
Pectinate
Imbricate
Petal
Diamond petal
Chevron

9. Scale Types
Mosaic
Chevron

10. Scale Types (cont)
Pectinate
Imbricate

11. Scale Types (cont)
Petal
Diamond Petal

12. HUMAN SCALES In order to visualize the scales
paint fingernail polish on a slide
place a hair on the polish
lift off the hair and observe the scale imprints
What pattern is seen in this slide?

13. Hair Cortex The cortex gives the hair its shape.
It has two major characteristics:
Melanin--pigment granules that give hair its color
Cortical fusi--air spaces, usually found near the root but may be found throughout the hair shaft

14. Hair Medulla
The medulla is the hair core that is not always present. The medulla comes in different types and patterns.
Types:
Continuous
Intermittent or interrupted
Fragmented
Absent--not present

15. Hair Medulla Patterns Uniserial Multiserial Vacuolated Lattice
Amorphous (without a distinct pattern)

16. HUMAN MEDULLA
Human medulla may be continuous, fragmented or absent.

17. RABBIT MEDULLA
Rabbit medulla is different depending on the type (location on the rabbit) of hair. The one to the left is multiserial. The one to the right is a uniserial ladder and is found in guard hair.

18. Medullary Index
Determined by measuring the diameter of the medulla and dividing it by the diameter of the hair.
Medullary Index for human hair is generally less than 1/3.
For animal hair, it is usually greater than 1/2.

19. Hair Comparison Color Length Diameter
Distribution, shape and color intensity of pigments granules
Dyed hair has color in cuticle and cortex
Bleaching removes pigment and gives yellow tint
Scale types
Presence or absence of medulla
Medullary type
Medullary pattern
Medullary index

20. Collection of Hair Evidence
Questioned hairs must be accompanied by an adequate number of control samples.
from victim
possible suspects
others who may have deposited hair at the scene
Control Sample
50 full-length hairs from all areas of scalp
24 full-length pubic hairs

21. Hair Toxicology Advantages:
Easier to collect and store
Is externally available
Can provide information on the individual’s history of drug use.
Collections must be taken from different locations on the body to get an accurate timeline.

22. HAIR TESTING Procedure
Collect an adequate sample, cut as closely to the scalp as possible.
Wash the hair to remove lipids, oils, cosmetics and any drugs adhering to it
Cut it into one centimeter sections
Place hair in a digesting solution
Screening test--antibodies are added to the hair that bind with the drugs. If this shows that drugs are present:
A confirmation test is done by gas chromatograph and then a mass spectrometer.

23. Fiber Evidence
NOTE: Fabric is the type of material and fibers are the “threads” that make up the fabric
The use of fiber evidence in court cases is used many times to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers were the entire case. Williams was convicted in 1982 based on carpet fibers that were found in his home, car and on several murder victims. Although this case is unusual, fibers are generally considered of greater value as evidence than that of rootless hairs since they may contain a greater number of variables, thus showing more individual characteristics.

24. Polymers
Synthetic fibers are made of polymers which are long string of repeating chemical units.
The word polymer means many (poly) units (mer).
The repeating units of a polymer are called monomers.
By varying the chemical structure of the monomers or by varying the way they are weaved together, polymers are created that have different properties.
As a result of these differences, forensically they can be distinguished from one another.

25. Analysis of Fibrous Material
U.S. Department of Justice
FBI, April 1999

26. Types of Fibers Natural Synthetic Silk Polyester Cotton Rayon Wool
Mohair
Cashmere
Synthetic
Polyester
Rayon
Nylon
Acetate
Acrylic
Spandex

27. Classification Classified according to their origin:
Vegetable or cellulose
Animal or protein
Mineral

28. Cellulose Fibers
Cotton--vegetable fiber. Strong, tough, flexible; moisture absorbent; not shape retentive
Ramie--vegetable fiber. Less flexible than cotton so its often blended with cotton
Rayon--first man-made fiber; soft, lustrous, versatile fiber
Cellulose esters--cellulose is chemically altered to create an entirely new compound not found in nature.
Acetate--less expensive, less polluting than rayon

29. Fiber Comparison Can you tell the difference(s) between the cotton on
the left and the rayon on the right?

30. Petroleum Plastics (Made from derivatives of petroleum, coal and natural gas)
Nylon--most durable man-made fabric; extremely light weight
Polyester--most widely used man-made fiber
Acrylic--provides warmth from a lightweight, soft and resilient fabric
Spandex--extreme elastic properties

31. Protein Fibers
Wool--animal fiber coming most often from sheep but may be goat (mohair), rabbit (angora), camel, mink, beaver
Silk--animal fiber that is spun by a silk worm to make its cocoon; fiber reflects light and has insulating properties
Wool Fibers (400X)

32. Mineral Fibers
Asbestos--a natural fiber that was used in fire-resistant substances
Metallics (mylar)--a manufactured mineral fiber
Fiberglass--another manufactured mineral fiber

33. Fabric Production
Fabrics are composed of individual threads or yarns, made of fibers, that are knitted, woven, bonded, crocheted, felted, knotted or laminated. Most are either woven or knitted. The degree of stretch, absorbency, water repellence, softness and durability are all individual qualities of the different fabrics.

34. Woven Fabric
Woven fabric are made by interlacing warp (lengthwise) and weft (filling) yarns. Warp run the length of the fabric and parallel to the selvage which is the edge of the fabric. Weft cross over and under the warp threads.
Types include:
Plain
Twill
Satin

35. Woven Fabric PLAIN Simplest and most common weave
Warp and weft pass under each other alternately
Create even patterns of 1/1 and 2/2
Design resembles a checkerboard

36. Woven Fabric
TWILL
Create by passing the warp yearn over one to three weft yearns before going under one
Makes a diagonal weave
Design resembles a stair steps
Denim is the most obvious example

37. Woven Fabric SATIN The yarn interlacing is not uniform
Creates long floats
Interlacing weave passes over four or more yarns
Satin is the most obvious example

38. Knitted Fabric
Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination. Either way, the yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric..
Diagram:

39. Identification and Comparison of Fibers
Microscopic examination
Color--compositional differences in the dyes
Fibers surface--delustering particles that may be added by manufacturers
Microspectrophotometer--compares fiber colors through spectral patterns
Chromatography--gives a more detailed analysis of the dye composition

40. Identification and Comparison of Fibers (cont.)
Polarizing microscope
can be used to determine the refractive indices of various fibers. The fiber is immersed in a fluid that has a comparable refractive index. The disappearance of the Becke line is observed under the microscope.
In addition, fibers will absorb infrared light in a characteristic pattern. This can be observed through the use of an infrared microspectrophotometer and a microscope.

41. Collection of Fiber Evidence
Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged.
Make tape lifts of exposed skin areas of bodies and any inanimate objects
Removed fibers should be folded into a small sheet of paper and stored in a paper bag

42. Uniqueness Establishing Individual Characteristics
If there is only one source for the transfer material with a controlled environment where the contact took place
If there is contamination of several different materials from surface onto surface two
If there is a method available to characterize the material, such as applying DNA
Otherwise, trace evidence would have only class characteristics.

43. Man, I was nailed when those forensic guys found fibers
from the kid’s math assignment in my teeth.