1 chapter 5 hair. 2 class evidence circumstantial evidence – lots of people have same hair color...

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Chapter 5 Hair

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Class evidence

• Circumstantial evidence – lots of people have same hair color• Places someone at the scene• Only becomes individual evidence if

skin or cells attached – then DNA is the individual evidence

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“Hair” are the facts…• Avg human body has ~ 5 million hairs – most

fine, down like

• Hairs are continuously shed and renewed at a rate of 100/day so not surprising that it is at a crime scene

• Head hair:• Blonds have ~ 120,000• Black, brown ~ 100,000• Redheads ~ 80,000

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Hair Morphology• Protein polymers (molecule consisting of many identical

repeating units)

• Hair grows from a follicle (tube-like structure in the dermis) which is linked to the blood supply so whatever substances are taken into the body they are distributed to the hair growing at that time

• Hair shaft extends out through the epidermis and ends at the tip

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Hair Morphology: Hair Shaft

• Cuticle – clear outer covering; tough overlapping scales

• Cortex – keratin molecules that run parallel to the length of the shaft; contains pigment that makes hair black, brown, yellow, red; no pigment = white, gray; cortical fusi - air spaces in the cortex that have to be seen w/ high power microscope.

• Medulla – row of cells along center of cortex; human hairs have either fragmented or no medulla except Native Americans and Asians – continuous medulla

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Hair Shape• Depends on cross section of shaft • Round – straight hair• Oval - curly• Crescent-shaped – kinky

• Can also be twisted or undulated (slightly wavy)

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Hair Growth

• Coarser hairs grow slower and fall out less frequently• ~ 1cm per month• Replaced every 3 to 5 years

• 3 stages of growth:

• Anagen – 80-90% of hair follicles at any one time

• Catagen – intermediate stage; lasts about 3 weeks

• Telogen – 8-10% of hair follicles; lasts 2-6 months; loss of hair

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Anagen hair root

telogen hair root

Catagen hair root

Recently cut hair

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Hair appearance• How would the following appear different:• Recently cut• Hair in brush• Hair pulled out from scalp• Cut 2-3 weeks ago

• Colored hair• Unconditioned hair• Split ends • Over heated (blow dryer, curling iron, etc.)

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So what exactly can be determined from hair evidence?

• Whether the source is animal or human• Racial origin (sometimes)• Location on source’s body• If hair has been chemically treated (dyed, permed,

straightened)• Color• If hair was forcefully removed

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Hair as a chemical indicator• Chemicals enter cortex of

the hair• Drugs• Metabolites (product of a

substances after a chemical reaction – after body metabolizes the chemical)

• Vitamins• Poisons (heavy metals –

arsenic, lead, mercury)• Oils in hair may contain

substances from environment – smoke from crack; (risk of false positive)

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Hair from a crime scene

1. Determine human or animal – what type of animal

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2. Determine race