Forensic Science: Hair & Fiber Unit: Lab #1: Hair Analysis
Why Hair Can Be Used in a Forensic Investigation
Human hair is one of the most frequently found pieces of physical evidence located at the scene of a violent crime and
can provide a substantive link between the criminals and their act. When it is properly collected at the crime scene with
observation of proper controlling factors, hair can best provide strong colloborative evidence for placing an individual at
the sight of a crime. Hair is valuable evidence, since it does not decompose as rapidly as most other human tissues or
body fluids. It therefore remains intact long after other types of personal evidence have become useless. It must be
remembered, however, that hair is class evidence and thus it is usually not possible to determine in a court of law that a
particular hair sample specifically came from a certain person. But with careful observation and analysis, the hair
sample often leads to other, more convicting evidence.
Hair samples are obtained from head, facial, or pubic locations. These hairs may be of different structure, texture, and
color. Hence, when comparison is made to the sample of hair from a suspect, it is necessary to collect an adequate
number of sample hairs from different locations on their body. At least 10-12 hairs from each possible location on
their anatomy are needed when making a proper comparison.
The criminologist is particularly interested in the matching of color, length, and diameter as well as determining the
presence or absence of a MEDULLA, and the distribution and color intensity of the pigment granules in the CORTEX.
Scale structure, medullary index, and medullary shape are also important in hair identification. Whether the hair has
been dyed or bleached can easily be determined. Even the approximate time of loss for the hair sample can be
approximated since it is generally accepted that hair grows approximately 5mm per day, or approximately one-half
inch per month.
Hair Structure
Human hair, and the hair of all mammals, grows from the hair follicle, a pore-like organ within the skin.
In gross structure, hair is made up of two distinct parts. The shaft of the hair projects from the skin, and it is this
portion that we readily see. The root, which is embedded in the follicle, lies
below the epidermis, well within the dermal layer of the skin. The root of a
mature human hair is similar in appearance to a flower bulb. Other species may
show different root types, and these are often used to determine the species of
origin. In cross section, the hair shaft
is comprised of three distinct layers. It is the variation within these three layers that
the forensic examiner notes in comparing human hair. (See Diagram to the right).
The outermost layer of the hair shaft is the cuticle, made up of layers of scales,
which cover the hair shaft. Examination of these scale patterns plays an important
role in determining species and is also used in the comparison of human head
hair. The three basic scale patterns — coronal, pinous, and umbricate — are
shown in Diagram below. Note that the scales always point toward the tip of
the hair.
Tip End
Corona!
(Mouse)
Spinous
(Cat)
Imbricate
(Human)
The core, or center of the hair shaft is called the medulla. This structure is not always present in the hair shaft, but
when present it shows great variation. This makes the medulla very useful in species identification. As shown in
Diagram below, the medulla's appearance can be classified as fragmented, intermittent, or continuous.
Fragmented Intermittent Continuous
The basic structure of the medulla also can vary. Some of the more common medulla types are pictured in Diagram
below. It should be noted that the medullary index, (the relative size of the medulla compared to the entire hair
shaft), is rarely used as a point of comparison.
Surrounding the medulla, and generally comprising the greatest area of the human hair shaft, is the cortex. Within the
cortex are other structures of interest to forensic scientists. Pigment granules (melanin), which help to give hair its
color, appear as small dark objects. The location and distribution of these structures can be used for some species
identification. Cortical fitsi are actually air spaces within the cortex.
Usually found near the root (proximal) end of the hair shaft, these air spaces can also be found throughout the length
of the hair shaft. This is usually the case with light-colored or blond hair and is probably a contributory factor to that
hair's appearance. (See Diagram below).
The hair diameter, its properties of curl, kink, or straightness, and the cross-section appearance of hair can often be
used to determine the race of origin. These are generalities applied to the examination of head hair, since the hair
of people of mixed racial origin may not present a readily identified geometry.
Since, in our investigation, we are most concerned with the analysis of hair. To examine hair, it is important to
produce a scale cast and properly prepare a WHOLE MOUNT slide. This will then be observed under
magnification and compared, to the best that our equipment will allow. Ideally, a comparison microscope or a
microscope camera should be used to adequately compare two hair samples side-by-side. But in most cases a standard
laboratory microscope can be used.
Forensic Examination: Determination of Species Part 1
A. Preparation of Scale Casts for Determination of Species
After making careful observations and comparing the hairs with the diagrams on your Student Diagram
Chart, you should be able to identify the species of each unknown sample.
1. Label slides based on the animal or color of hair. Coat a center section of each of the microscope slides
with a thin layer of nail polish.
2. Then take 3 or 4 single hairs of each sample and lay them in the nail polish on the slide in a radial pattern with
one end sticking out of the polish. Let the polish stand for a few minutes so that it begins to harden, i.e.
becomes 'tacky'. Pull one hair up off the slide with a pair of tweezers or tongs, using the free end of the
hair. Wait 30-60 seconds and pull out the second hair. Proceed in the same manner until all of the hairs are
removed from the slide. Allow the polish to completely harden.
3. Look at the slide under a transmitted light microscope at 40x and 100x. Which hair successfully gave a
scale pattern? This will give you an idea of the consistency of the nail polish that is necessary to give a good
scale pattern.
4. Repeat with all samples.
5. While observing the samples microscopically, fill in the data on a data sheet in your notebook. It should look
something like this:
Sample
Color
Length
Appearance
(diameter,
curl, etc.)
Distal End
Description
Proximal
End
Description
Scaling
Medulla
Appearance
Cortex
Appearance
Cortical
Fusi &
Melanin
6. Classify the scale patterns as to their type and record answers on your worksheet.
Preparation of Whole Mounts and Comparison of Human Hair Samples Part 2
A single human hair is often found at the scene of a crime, and the laboratory must compare this evidence with hair
samples obtained from various suspects. In the crime laboratory, a comparison microscope is used to compare
questioned and known hair samples. Since your laboratory does not have this specialized equipment, you will
use your evidence sheets to compare the hair samples.
Procedure
Complete the following procedure for each of the hair samples.
1. Place a clean microscope slide on a flat surface. Label the slide according to the hair sample you will be
working with.
2. If longer hair will be used and observed along the whole hair shaft, use a 24 x 40 mm cover slip.
3. Then wet a small surface of the slide with the mounting medium.. Place the hair sample in this wet area
to secure the hair in place. Use about 5 hairs.
4. To observe a whole hair 8 inches or longer, place the hair on the slide in a figure-eight pattern and use
three areas of tacking, as shown below. Make sure that the ends and shaft are restrained enough to be
completely covered by the cover slip.
5. Holding the cover slip horizontally in one hand, add the mounting medium to the cover slip. Use about 2 drops
of medium for small cover slips and about 4 drops for larger cover slips.
6. Quickly invert the cover slip onto the slide, starting at one edge and pivoting the other edge downward as
illustrated below. This helps eliminate air trapped in the hair mount.
7. If the mounting medium does not completely fill the cover slip, add more along the side, as illustrated below. The
medium will be attracted by capillary action.
8. Observe the slides under a light microscope at approximately 40x.
9. Then examine the roots and sketch and record your observations in your notebook. Note: Some
variations may exist within a single hair sample.
10. Scan the lengths from the proximal end (root) to the distal end (tip) for several of the hairs and observe the
medullary characteristics. Record your observations in your notebook, for each hair sample. Your chart
should look something like this:
Sample
Color
Length
Appearance
(diameter,
curl, etc.)
Distal End
Description
Proximal
End
Description
Scaling
Medulla
Appearance
Cortex
Appearance
Cortical
Fusi &
Melanin
Unknown Forensic Hair Comparison Part 3
In this examination each team of two students will mount three human hair samples. You will also mount an
"Unknown" hair that has been selected from the three samples by your instructor.
Materials Included:
Three human hair samples
Slides
Mounting medium
Small envelopes
Cover slips
Unknown hair
Materials Needed but not included:
Microscopes
Microscope camera
Procedure:
1.
Working in teams of two, obtain D, E, and F hair sample, as well as the unknown from your instructor.
2.
Using the mounting procedure described earlier, mount each sample as well as the unknown on
separate slides.
3.
Examine the samples visually and microscopically.
4. Record on separate sheet of paper all information to compare the samples.
5. Then you will determine whether the "unknown" hair is a match with any of the original three samples.
Unknown Forensic Hair Comparison Part 4
BackgroundInformation
Janis Menendez owns a cat, Stingray, who has starred in several commercials for Flower Fresh Kitty Litter.
Before Stingray was a famous cat, she belonged to Penny Jenkins, a full-time college student. Janis agreed to take
the cat from Penny several years ago when Penny was too busy to properly care for her. Since Stingray's recent
introduction to the world of television, she has earned her owner about $750,000.
On April 2, Ms. Menendez calls San Diego 911 to report that Stingray has been stolen. Menendez states
that she was in the family room watching the news while Stingray ate her dinner in the kitchen. Menendez
heard a door open, and then a loud screech from the cat. By the time she got to the door, Stingray was gone.
All Ms. Menendez saw was a medium-sized car speeding away from her home.
Police who investigate the scene of the crime find no evidence of a forced entry at the kitchen door.
Therefore, it is concluded that whoever opened the door and stole Stingray had a door key. Police ask Ms.
Menendez for a list of people who drive a medium-sized car and have a key to her house. Her list includes:
a. Joe Menendez, her husband, who loves dogs and is allergic to cats.
b. Bill Branson, a cosmetic salesman whose products are boycotted by Ms. Menendez because they are tested
on animals. Susan Branson, his wife, is one of Janis's best friends and knows where the spare key to her
house is hidden.
c. Jill Rayburn, a neighbor and cat hater who has poisoned several cats in the neighborhood. kitchen
window looks into Janis's back yard, Jill may have seen Janis hide her spare key.
d. Brandy Bledsoe, the maid who often complains that Stingray sheds hair all over the house. Brandy has her
own key.
e. Penny Jenkins, Stingray's previous owner and part-time sitter. Penny keeps a key for those occasions when
she cat-sits.
Materials
Envelopes containing hair samples taken from the suspects' cars:
A — Joe
B — Bill
C — Jill
D — Brandy
E — Penny
Compound-light microscope
5 slides
5 cover slips
Small beaker of water
Dropper
Small, transparent ruler
Procedure
1. Create a data chart in your notebook looking something like this:
Sample A
Sample B
Sample C
Sample D
Sample E
Observations
Scales (if present)
Diameter of medulla
Diameter of hair
Medullary ratio (type)
Cortical Fusi Present
Pigment
Hair Length
Tip condition:
Smooth, split,
blunt, crushed,
frayed
Condition of root:
Absent, rounded,
tapered
2. Prepare a wet-mount slide of a piece of hair from Envelope A. Follow the procedure above.
3. Examine the hair under low, medium, and high power. Draw what you see on high power in the
chart.
4. Determine the medullary ratio of each hair by measuring the diameter of the medulla and the
diameter of the hair. Express these two numbers as a fraction in the Data Table.
5. Fill in the rest of the information in the chart.
6. Repeat steps 2 through 5 for hair samples in envelopes B, C, D, and E.
Postlab Questions
1. Based on information in your sketches and in the Data Table, which hair sample(s) belong to
Stingray?
2. How can you tell human hair from animal hair?
3. When examining the hairs under the microscope, were the cuticle scales clearly visible?
Describe their appearance.
4. How can investigators use hair evidence to help solve a crime?