1. FORENSIC SCIENCE Trace Evidence
5/1/2018
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 victim and the crime scene.
From hair the following can be determined:
Human or animal
Race
Origin
Manner in which hair was removed (naturally shed, gently pulled out, or aggressively ripped out)
Treated hair (perm or dye)
Drugs ingested

5. Hair and Skin

6. Structure Think of each strand of hair as a very thin pencil.
The medulla is the “lead”.
The cortex is the “wood”.
The cuticle is the “yellow paint”.

7. Hair Structure

8. Hair Structure

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

10. Cuticle Types
Mosaic Pectinate Imbricate Petal Diamond Petal Chevron

11. Cuticle In order to best see the cuticle
paint fingernail polish on a slide
place a hair on the polish
lift off the hair and observe the cuticle imprints
Can you identify the pattern seen in this slide?

12. Microscopic view of human cuticle

13. Hair Cortex The cortex gives the hair its shape.
It is made of cortical cells that give bulk, shape, elasticity and curl to the hair.
It has two major characteristics:
Melanin--pigment granules that give hair it’s 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.
It is not always present.
It comes in different types and patterns.
The human medulla may be continuous, fragmented or absent.
Continuous
Intermittent or interrupted
Fragmented
Absent - not present

15. Intermittent Absent Continuous

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

17. Double Medulla

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

19. Hair Growth Terminology Anagen: Catagen: Telogen: hair that is growing
hair at rest
Telogen:
hair that is dying

20. Normal Hair Growth
About 90 percent of the hair is growing (anagen phase) at any one time
The growth phase lasts between 2 – 6 years.
Scalp hair grows about ½ inch per month.
As people age their rate of hair growth slows.
Ten percent of the hair is in a resting phase (catagen phase).
This phase lasts 2 – 3 months.
At the end of its resting stage the hair is shed.
When a hair is shed (telogen phase), a new hair from the same follicle replaces it and the growing cycle starts again.
Most hair shedding is due to the normal hair cycle, and losing 50 to 100 hairs per day is expected and is no cause for alarm.

21. How/When Did It Leave?
                                               
                      
Telogen
Anagen

22. Ethnicity
Asian
Black
Asian
White

23. Cross-Sections
African American
Caucasian
Asian

24. Dyed Human Hair

25. Root Band

26. 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.

27. 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

28. 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

29. 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.

30. 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 to identify the specific drugs.

31. Buckling
               
Buckling is a disruption of the hair shaft demonstrating itself as an abrupt change in direction with or without a slight twist.

32. Razor Cut
A razor cut hair is angular and very straight or clean.

33. Egg Case
Head louse egg case on human hair.

34. Lice
wingless, usually flattened, bloodsucking insect that is parasitic on warm-blooded animals

35. Magnified laser image on human hair.
Wow
Magnified laser image on human hair.
Magnified photo of a human hair sculpted by an Excimer laser (used in LASIK eye surgery).