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FORENSIC SCIENCE

Trace Evidence

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Introduction Trace Evidence--any small pieces of material, man-made or

naturally occurring.

Trace evidence (in the absence of DNA) is considered class

evidence. As early as the 1879, Dr. Rudolph Virchow

realized that hair could only be used to eliminate suspects,

but was not likely to conclusively link anyone to a crime.

“The appearance of the victim’s hair is not inconsistent

with having come from the accused.”

Remember me?

Trace evidence: Class evidence

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Most common examples:

Hair

Fiber

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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 act (Locard’s

Principle).

From hair one can determine:

Human or animal

Race

Origin

Manner in which hair was removed

Treated hair

Drugs ingested

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DNA

The hair shaft contains abundant

mitochondrial DNA or mtDNA--inherited

only from our mothers. It can be typed by

comparing relatives when nuclear DNA is

not available.

It is commonly thought that only the root

contains nuclear DNA. However, in rare

instances, some nucleated cells called

corneocytes can also be extracted from the

normally degraded hair shaft.

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Hair Morphology

The Study of Structure and Form

Parts of the hair

Shaft--part of the hair

that sticks out of the skin

Root--lies below

the epidermis

Follicle--structure from

which the hair grows

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Hair Growth Terminology

Anagen--hair that is growing

Catagen--hair at rest

Telogen--hair that is dying

Length--00.5 mm per day or 1 centimeter

per month; approximately one half inch

per month

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Hair Cuticle The cuticle is the outermost layer of hair which is

covered with scales. Scales also always point

toward the tip of the hair.

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HUMAN SCALES

In order to visualize the

scales

– paint fingernail polish

on a slide

– place a hair on the

polish

– lift off the hair and

observe the scale

imprints

What pattern is seen in

this slide?

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Scale Types Imbricate

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Scale Types

Mosaic Chevron

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Scale Types (cont)

Pectinate

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Scale Types (cont)

Petal Diamond Petal

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Hair Cortex

The cortex gives the hair its shape.

It has two major characteristics:

Melanin--pigment granules that give hair its

color

Cortical fusi--air spaces, usually found near the

root but may be found throughout the hair shaft

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The medulla is the hair core that is not always

present. The medulla comes in different

types and patterns.

Types:

Continuous

Intermittent or interrupted

Fragmented

Absent--not present

Hair Medulla

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Hair Medulla Patterns

Uniserial

Multiserial

Vacuolated

Lattice

Amorphous (without a distinct pattern)

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HUMAN MEDULLA

Human medulla may be continuous, fragmented or

absent.

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RABBIT MEDULLA

Rabbit medulla is different depending on the type

(location on the rabbit) of hair. The one to the

left is multiserial. The one to the right is a

uniserial ladder and is found in guard hair.

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Medullary Index Determined by measuring the diameter of

the medulla and dividing it by the

diameter of the hair.

Medullary Index for human hair is generally less than 1/3.

For animal hair, it is usually greater than ½.

Cats medullary index ratio is very high-higher than dogs!

Compare below-which side is cat and which is dog?

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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

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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

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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.

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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.