Forensics - Unit 2 ( Trace Evidence - Hair and Fiber)

What is trace evidence?

• any small piece of material (natural/man-made), came from a larger piece of evidence

  • ex. gunpowder, hair, fiber 

Why is hair such a valuable resource as evidence?

• Hair is abundant

  • if the hair contains a follicular tag, then that hair contains DNA

What are the 6 facts that can be determined by observing hair?

1. human or animal

2. race

3. origin (where on the body the hair came from)

4. manner in which the hair was removed

5. treated hair

6. drugs ingested 

What is the difference between class evidence and individual evidence?

• Class Evidence

  • evidence that could be pointed to multiple people

• Individual Evidence

  • evidence that can only be pointed to one person

What turns hair from class evidence to individual evidence?

• if the hair has a follicular tag, then that piece of hair contains DNA

What is a hair follicle?

• the organ from which the hair grows (source of DNA)

What is the follicular tag? When and where can it be found?

• What → filmy stuff around the root that contains DNA

• When → hair that has been forcibly removed AND contains the root - during the anagen stage

• Where → the root 

What are the 3 stages of Hair Growth?

1. Anagen

2. Catagen

3. Telogen 

What happens during Anagen?

• when the hair is alive, growing, and healthy 

• only time to get the follicular tag

• majority of your hairs lifetime

What is Catagen?

• transition between growth and rest

• the hair continues to grow, just at a slower rate

• the hair is preparing to fall out

What is Telogen?

• hair growth has ended 

• hair will fall out the easiest (kind of like when your hair sheds)

What are the 3 layers of hair?

1. Cuticle

2. Cortex

3. Medulla 

What is the cuticle?

• outer layer of hair

• covered in scales (can determine what animal the hair came from) 

What is the cortex?

• made up of cortical cells

• responsible for giving the root shape

What is the Medulla?

• central canal  running through he middle of the hair 

  • not all human hair has a medulla

  • BUT every animal has a distinct medulla pattern

What can we learn from observing the cuticle scales?

• what animal (cat, dog, human, or rodent) has the hair came from

What direction do the scales point to?

• The scales point to the tip of the hair.

What scale pattern do humans have?

• imbricate 

What is melanin and where is it found?

• pigment that gives your hair color

  • found on the cortex

What is cortical fusi?

• air spaces

• normally found near the root/spreads throughout the shaft

What can we learn from observing the medulla?

• Potentially what ethnicity someone is

• What type of animal the hair comes from

What are the 4 medulla pattern types?

1. Absent

2. Fragmented

3. Interrupted/Intermittent

4. Continuous

What is the medullary index?

• measures what percentage of hair is medulla 

  • Humans → less than 1/3

  • Animals → more than ½ 

What charcateristic of hair morphology helps to determine race?

• shape of the hair cross sections 

  • round → Asian (straight)

  • oval → European (wavy)

  • elliptical - African (kinky)

What is needed in order for a crime scene hair to be useful as evidence it must be compared against…”

• a number of control samples 

Who must the police collects hair fron?

1. victim

2. anyone who may have been around the crime scene

3. possible suspects

How much ahir quantifies as a variable control sample?

• 50 full-length hairs from all over the head

• 24 full-length public hairs 

Multiple fibers are wrapped together to make a ___?

• thread/ yarn

Multiple threads are woven together to form a ___?

• fabric

What is it called when yarn moves up and down the fabric?

• lengthwise yarn

• warp 

What is it called when the yarn runs from left to right?

• crosswise yarn

• weft

What is the definition of fiber?

• any small, elongated pieces of material used to manufacture

What are the three main types of weave patterns?

1. plain weave —> linen

2. twill weave —> denim

3. satin weave —→satin

What is a plain weave?

• a checkerboard-like appearance

• threads alternate from over to under to over 

• seen in clothing like button-down shirts and linen

What is a twill weave?

• yarn is passed over one to three weft yarns before going under one yarn

• used for materials that are less flexible

• seen in denim

What is a satin weave?

• the yarn interlacing is not uniform

• creates long floats

  • areas when fibers don’t interlace

• seen in satin

Which fibers are naturally occurring?

• animal - protein

• plants - cellulose

• excrement - silk

• mineral - asbestos and fiberglass 

Which fibers are man-made?

• regenerated —> rayon

• synthetic —> teflon, dacron

• petroleum —> polyester 

• mineral —> asbestos, fiberglassdf

What characteristic will help you identify protein fibers under a microscope?

• a medulla pattern and/ or scale patterns

What will a cotton (cellulose) fire look like under the microscope?

• a twisted fiber

What do mineral fibers look like under the microscope?

• long, thin, and needle-like 

What is a common source of excrement fiber?

• made from waste products 

Why can’t you use microscopic analysis to help identify synthetic fibers?

• because the fibers look exactly the same 

Where can you find petroleum fibers?

• textiles →spandex, nylon, polyester

• plastics 

• rubbers → tires, rubber bands, shoe soles

• adhesives

How are regenerated fibers produced?

• starts naturally occurring

• the fabric gets melted down, pushed through a spinneret,

• the fiber is cooled down into its final fiber shape

What is a polymer?

• basic chemical substances of all synthetic fibers, long-chained molecules

What are polymers made of?

• monomers 

What is the process of rearranging monomers called?

• polymerization

Why are chemical tests needed to differentiate