1. Forensic Science Hair Analysis

2. Hair is chemically stable especially when compared to other physiological materials such as blood, semen, or any other body fluid. Because hair is strongly resistant to decomposition, makes hair a nearly ideal type of physical evidence.

3. Hair at the Crime Scene Hair left by criminal during crime can be used to corroborate other evidence found during the course of an investigation. Hair might not by itself provide a positive identification, but c an narrow the pool of suspects. Hair is encountered as physical evidence in a wide variety of crimes

4. Hair Hair is part of integumentary system and grows out of a structure called the hair follicle. The root of the hair is embedded in the follicle and the shaft extends above the surface of the skin.

5. Hair The hair shaft is composed of three layers –Outer cuticle –Cortex –Central medulla Hair grows at a rate of approximately 1 cm per month

6. Cuticle Outer covering of hair Resistance to chemical and physical decomposition is due to cuticle Formed of cells that flatten, die and become keratinized to form overlapping scales that appear as small shingles Scales always point toward tip of the hair Great variety of scale patterns on hairs from different locations on the human body –Scales not useful for individualizing human hair –Are important in identification of animal species

7. Examples of Human Cuticle Electronmicrograph of healthy hair Severely damaged hair cuticle

8. Scales found on Mink hair

9. Diagram of Scale Pattern of Deer Hair Photomicrograph of Scale Pattern of Deer Hair

10. Cortex Within the protective cuticle Made up of spindle-shaped cells aligned parallel to the shaft axis Within cortical cells are pigment granules that give the hair its characteristic color Color, shape and distribution of the pigment granules vary between individuals Can examine features microscopically after hair is mounted in a liquid medium with refractive index similar to that of hair –When mounted in such medium, amount of light reflected off the hair’s surface is reduced, while amount of light penetrating hair is increased –Enables internal features to be seen

11. Photomicrograph of Pigment Distribution in Human Hair Figure 98. Photomicrograph of Pigment Distribution in Red Human Hair

12. Medulla Formed from collection of cells that appears as a central canal running the length of a hair In many animals, the canal is the most visible feature, making up more than half of hair’s diameter Width of medulla in comparison with width of hair provides way to classify hair from different animals –Medullary index Provides distinctive characteristic Expressed as a fraction

13. Medulla In humans, medulla usually absent or fragmented Rarely continuous –Except many individuals of Asian descent Nearly cylindrical in human Varied shapes in animals –Cat – string of pearls –Deer – spherical cells that occupy entire hair shaft

14. Diagram of Medullas Photomicrograph of Multiserial Ladder Medulla Photomicrograph of Uniserial Ladder Medulla

15. Forensic science investigators determine the medullary index of hair which is the diameter of the medulla relative to the diameter of the hair, expressed as a fraction. Humans have a medullary index of less than 1/3, and the medullary index of animals is 1/2 or greater. Hair Characteristics

16. For Identification Most important morphological features –Scale structure –Medullary index –Medulla shape Also interested in matching overall hair color, hair length, diameter, types of medulla, distribution, shape and color of pigment granules in cortex

17. Colored Hair Dyed hair – presence of “color” in cuticle and throughout cortex Bleaching – removes natural pigment and gives yellowish tint

18. Scale Casts Use latex to create “mold” of hair Remove hair after latex dries Able to see impressions of individual scales –Identify general shape of scale –Identified if jagged or smooth exposed edge of scale Prepared at least 24 hours ahead of time

19. Whole Mount Use Kleermount © to mount hair to slide Allows observation of internal structures –Pigment granules in cortex –Air spaces –Shape of medulla Prepared at least 24 hours prior to observation

20. Wet Mount Use water and cover slip to mount hair for observation Look at –Color –Texture –Condition Prepared immediately before making observations

21. Hair vs. Fiber? The easiest way to differentiate between hairs and fibers is by using a light microscope. –A PLM (polarized light microscope) can be useful but not necessary. –A PLM is more useful when you need to tell the difference among types of fibers: such as cotton, silk, rayon, polyester, nylon, and wool, etc. –When you look at hair under microscope, is possible to see various structures that are different among similar types of hair, and among different classes of hair. –Fibers and hairs are very different when they are viewed under the microscope.

22. Gross features Such as color, texture, degree of curl or wave are examined with unaided eye and low power microscope. Specific characteristics of hair by race are described in the table below RaceCharacteristic CaucasianStraight to wavy, evenly distributed pigment granules, fragmented medullae or absent of medullae, cross section oval/round, fine to coarse pigment AsianDense pigment distributed evenly, cross section round, hair shaft coarse and straight, presence of continuous medullae African American Curly, heavy pigment distributed unevenly, variations in diameter, fragmented medullae or absent of medullae

23. A strand of hair has three layers: cuticle, cortex, and medulla. –The outermost covering, cuticle consists of hard overlapping scales that point toward tips end. –The cortex contains pigment granules that give hair its color. –The medulla is a hollow tube within the hair, which may be present or absent. Depending on the hair, this hollow tube is continuous, or fragmented. The examiner compares above factors: color coarseness, granule distribution, hair diameter, and presence or absence of a medulla.

24. http://www.fbi.gov/hq/lab/fsc/backissu/jan2 004/research/2004_01_research01b.htm