Hair Evidence

Forensic ScienceMr. Glatt, 2014-2015

Function of Hair

• All mammals have hair• Functions of hair include– Body temperature regulation and warmth– UV protection– Decrease Friction – Helps with sense of touch

Hair as Evidence• Hair is considered class evidence when the hair follicle is not

attached– Investigators can identify a subgroup or class of people who share

similar hair characteristics

• When follicle is attached it becomes individualized evidence because DNA can be obtained– Skin cells and blood on follicle provide DNA

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Hair as Evidence, cont…• Hair is easily transferrable from crime scenes because it

adheres to fabrics in clothes, carpets, ect…– It often is transferred to other locations, this is called

secondary transfer• Secondary transfer is especially common with pet/animal hair

• Chemical testing of hair can also provide a history of the use of drugs and other toxins, indicate the presence of heavy metals, and even provide an assessment of nutritional deficiencies

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The Structure of HairHair Follicle

• Hair Consists of two Parts– Hair Follicle- club shaped

structure that extends into the dermal layer of skin• Generates hair shaft• Sebaceous (oil) glands

condition hair with oils• Blood vessels at end for

growth, repair

The Structure of HairShaft

• Shaft– Composed dead

celled filled with 2 proteins• Keratin is what gives

hair it’s strength• Melanin is what gives

hair it’s pigmentation or color

What can hair samples can tell us?

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

permed, straightened)• Color and pigmentation • Presence of toxins or drug metabolites• Whether the hair was forcibly removed

–If so, follicle usually still attached

How hairs differ

• SHAPE- A cross section: circular, triangular, irregular, or flattened

–Shape influences the curl of the hair• TEXTURE- coarse or fine• COLOR-blonde, brown, black, red ect…• Hairs can differ, even hairs from the same parts of

the body–Distribution of Melanin (pigment granules)

• Hair From Different Parts of Body

Human hair varies on the body

• * one way to distinguish is by cross-section• * other ways to distinguish as well

• – Head • Usually circular or oval• Little variation in humans and more uniform

distribution of pigment

• – Eyebrows & Eyelashes• Circular and often have tapered ends

• Beard and Mustache• Tend to be thick and triangular• course and may have double medulla• Blunt tips from cutting or shaving

• Underarm• – Body Hair

•Oval or triangular• Blunt tip or may be frayed from abrasion

• – Pubic•Oval or triangular• buckling may be present, short and curly• Diameter may vary greatly

Treated Hair

• Bleaching –disturbs the scales on the cuticle and –removes melanin (pigment)–leaves hair brittle and yellowish

• Dyeing colors the cuticle and the cortex

Racial Differences

• • Broad, racial groups do exhibit some shared physical characteristics

• • But NOT applicable to all individuals in these groups–Therefore, •Individual hairs CANNOT necessarily be

assigned to any of these groups• • Age Determination

• Age can not be determined with any degree of certainty except for infant hair

– Infant hairs are fine, short in length, and have fine pigment

Using Hair in an Investigation

• Hairs must come from same area of the body–Comparisons must be made from same location

of the body• Hairs from even the same part of the body can differ

• Forensic hair comparisons generally either involve either head hair or pubic hair

–Head hairs- 50 full length hairs should be taken for comparison to hair in question

–Pubic haris- 25 full length hairs should be taken for comparison to hair in question

Microscopic ExaminationPotential Error

• Microscopic comparison of hair has long been accepted practice as approach to including or excluding suspects

– Can be subjective and is highly dependent of skills and integrity of analyst, and hairs being examined

– Before DNA it was relied upon more• FBI study conducted from 1996-2000

–a number of microscopic matches were shown incorrect when samples were subjected to DNA testing (about 11%)

Testing the Hair Follicle

• If hair is forcibly removed the entire hair follicle may be present along with very small amounts of

–Blood can be typed to determine blood type

*Still class evidence• DNA from follicle cells and hair root can be analyzed

individualized evidence• Often times microscopic analysis is completed first to

determine if is a possible match, more cost effective

Mitochondrial DNA in Shaft

• • Hair in shaft contains no nuclear DNA• • Hair in shaft does contain mitochondrial DNA• – Mitochondrial DNA passed down from mother,

originates from mitochondria from egg• • can exclude significant portion of the population

as potential contributors to the hair sample• • Cannot distinguish from individuals who are

maternally related• – Anybody on mother’s side of the family

Testing for Drugs in the Shaft

• • Human hair growths at a rate of 1.3 cm per (.44 mm per day)

• • Hair grows from skin, chemicals being excreted by skin become incorporated into hair

• • During testing, the hair is dissolved in an organic solvent and any substances incorporated in hair are released

• • A forensic chemist can then perform various tests to determine the presence of various substances

• – This analysis can provide evidence of poisoning or drug use