Forensic Analysis of Hair

How useful is hair in a forensic investigation?

• Used to back up circumstantial evidence and help place individuals at the crime scene.

• Hair without the follicle = class characteristics

• Hair with the follicle = individual characteristics (allows for DNA fingerprinting)

Morphology of Hair

Morphology - refers to color and structure

Hair grows out of an organ called the hair follicle

•the root is embedded in the follicle

•the shaft is the main part of the hair

•the tip is at the opposite end to the root.

Morphology of Hair

• Forensic scientists primarily examine the hair shaft, which is composed of three layers:

• a. Cuticleb. Cortexc. Medulla

Cuticle

•Outer surface of hair

•Reason that hair resists

changes in structure and

does not easily decompose

•Formed from overlapping scales that point towards the tip of the hair (formed from keratinized cells)

•Scales are more prominent on animal hair than human hair and can be used to ID the species

•Examined by comparison microscope or hair casts.

Examples of Cuticles

Cortex

•Main body of hair shaft

•Contains pigment granules

and possibly air bubbles

called cortical fusi

•Color, shape and distribution of granules are analyzed by criminalist

•Examined by placing hair on a microscope slide in a liquid with a similar refractive index

MedullaCentral canal running through the hair (not always present)

Medullary index – diameter of the medulla relative to diameter of entire hair (represented as a fraction)

•Humans approx. 1/3 or less

•Other animals 1/2 or more

0 1/10 1/3 1/2 9/10

Medulla Classification

Human: usually absent or fragmented

- can be continuous (Mongoloid)

Animal: usually continuous or interrupted

-many are also patterned (ex, cat = string of pearls)

-A database has been established containing the 35 most common

types of animals encountered. Can be searched by scale pattern or medulla type

Also:

Absent

Patterned

Examples of Medullas

Hair Shape

Straight Curly Kinked

Asian/ Caucasian AfricanCaucasian

No twist No twist Twists and undulates

RootAllows for hair growth

3 Stages of hair growth:

1. anagen – (up to 6 years) – follicle is actively producing hair

- roots have a flame-shaped appearance b/c attached to the follicle

- if the hair is pulled out at this stage, typically will have the follicular tag attached

2. catagen – (2-3 weeks) – hair growing still but slowly- roots have elongated appearance b/c root bulb shrinks

3. telogen – (2-6 months) – hair pushed out of follicle and shed

- root has a club shaped appearance

Stages of Hair Growth

Identification and Comparison of Hair:Steps the Forensic Analyst Takes

1. Determine if hair belongs to an animal or a human- EASY – use medulla/cuticle to ID species

2. Determine if human hair matches known samples- HARD – morphology/color differs w/in the same

person

Things examined by the forensic scientist

1. Compare color, length, diameter

2. Examine medulla, cuticle, cortex

– abnormal morphology can indicate disease or vitamin deficiencies

3. Try to determine if hair is dyed or bleached

a. Dyed hair – dye reaches into the cortex and cuticleb. Bleached hair – removes pigment so has yellow tint

Estimate time of dying possible since hair grows about 1cm/month

Common Questions

1. Can the area of the body the hair came from be determined?

2. Can racial origin, age and sex be determined?

4. Are there any ways to individualize hair?

3. Can it be determined if hair was removed with force or naturally shed?

Racial origin usually can be determined:• African American – kinky, dense, unevenly distributed pigments• Caucasian – straight or wavy, more evenly distributed pigments

Age and sex cannot be determined at this time

- Typically hair removed by force or with a brush has follicle still attached- Important consideration is how quickly hair is pulled out

- DNA technology – examining follicular tag or root when hair is in anagen phase

Collection of Hair

1. Need an adequate number of control samples from same area of body

2. Need to try and collect full length hairs from all over scalp

4. During an autopsy it is now routine to remove hair samples in case they are

needed later on.

3. Entire hair length should be collected since may change in color and morphology

Case Story

Recap of Analytical Techniques

Comparison microscope

Physical Properties

Temperature (melting point/freezing point)Weight/MassDensityRefractive Index

Chemical Properties

Color testsMicrocrystalline testsChromatographySpectrophotometryMass Spectrometry

Objectives

1. Learn the morphology and distinguishing features of hair

2. Compare various different types of hair under a microscope.

3. Analyze the medulla, cortex and cuticle of several hair samples.

4. Describe the hairs of several species of animals.

5. Describe the collection procedures for hair.