Hair Evidence Analysis

Hair as Evidence

1. Human hair is one of the most frequently found pieces of evidence at the scene of a violent crime.

2. Hair is not the best type of physical evidence for establishing identity. Because you can't prove they came from the same person without the root.

3. Hair can be used to rule out certain suspects or scenarios. It can also be used to support other physical evidence

How much hair is on the average human head

- About 250,000 hairs- are replaced over a 3-year cycle
- About 250 hairs are shed daily; about 100 are from the head.
- Blondes tend to have more head hairs than brunettes. - Redheads have the least.

Hair at a Crime Scene

- Hair is class evidence- bc it can't be linked to a specific person
-Hair can easily be left behind at a crime scene. It can also stick to clothes, and carpets, and be transferred to other locations. This is called secondary transfer.
- Secondary transfer is particularly common with animal hair.

Hair analysis may be helpful to determine the following

Human or animal origin
racial background of an individual
Body region from which the hair came
How the hair was removed
Chemical tests can provide a history of the use of drugs or nutritional deficiencies
When the follicle of a hair is present, DNA evidence may be obtained and it can lead to individual identification.

Collecting Hair

-fingers or tweezers to pick up visible strands of hair
- tape lift may be used to help collect hairs.
-large surfaces means that they can also be vacuumed.
-paper bindles or coin envelopes which should then be folded and sealed in larger envelopes.

Function of Hair

decrease friction
to protect against sunlight
sensory
camouflage
regulates body function

Structure of Hair

Is made of of two parts follicle and shaft

How to individualize hair

the root needs to be present

Hair Shaft Structure

It is made of keratin makes it flexible.
Hair shaft is composed of three layers cortex, medulla, cuticle

Cuticle

outermost layer of hair, Made of scales that overlap one another and point toward the tip end

Medulla

core of the hair. It can be a hollow tube, or filled with cells.
Forensic investigators classify hair into five different groups depending on the appearance of the medulla.

Five groups of the Medulla Pattern

continuous, interrupted, fragmented, solid, none

cortex

Middle layer of the hair
largest part of the hair shaft, contains pigment granules

Two main of pigments

Eumelanin- gives color to brown or black hair
Pheomelanin- produces the color in blonde or red hair

Differences in Hair

-The cross-section of the hair may be circular, triangular, irregular, or flattened, influencing the curl of the hair.
-The texture of hair can be coarse as it is in whiskers or fine as it is in younger children.

Hair from Different Parts of the Body

Head hair
Eyebrows and eyelashes
Beard and mustache hair
Underarm hair
Auxiliary or body hair
Pubic hair
Hair from the head and pubic region is most common at a crime scene.

Distal Tips

The appearance of the tip of the hair shaft is an important comparative characteristic.
If sufficient sample is available, it may be possible to identify the type of treatment and estimate the length of time since the last cutting.

Treated Hair

- When a person chemically treats his or her hair, traces of the chemicals used remain. Some of these changes are subtle and can be detected only by using a microscope.
- Bleaching hair removes pigment granules and gives hair a yellowish tint. It also makes hair brittle and can disturb the scales on the cuticle.

Racial Differences in Hair

-Human hair can be associated with a particular racial group based on established models for each group. Forensic examiners differentiate between hairs.
- Head hairs are generally considered best for determining race, although hairs from other body areas can be useful.

Types of Hair

-Caucasoid (European ancestry),
-Mongoloid (Asian ancestry)
- Negroid (African ancestry)

Animal vs. Human Hair

If the medullary index is 0.33 or less, the hair is from a human.
If it is 0.5 or more it is from an animal

Electron microscopes

provide incredible detail of the surface or interior of the sample, magnifying the object 50,000 times or more.

Neutron Activation Analysis

A useful technique that can identify up to 14 different elements in a single two-centimeter-long strand of human hair.
The probability of the hairs of two individuals having the same concentration of these different elements is about one in a million.