In any struggle between victim and attacker hairs and fibres from
one are inevitably transferred to the other. The importance of hair
in criminal investigation was realised at an early stage in the
development of forensic science, and one of the first scientific
papers on the subject was published in France in 1857. By the early
1900s microscopic examination of hair was well established, and in
1931 Professor John Glaister published his Hairs of Mammalia from
the Medico-legal Aspect, which became a standard reference work.
Hair can provide crime investigators with important
clues. Apart from burning, hair is virtually indestructible. It
remains identifiable even on bodies in an advanced state of
decomposition or attached to objects after a crime has been
committed.
The forensic scientist using a microscope can make
even a single head hair yield information about the race, sex an age
of its owner, and while hair does not have the same individual
character as a fingerprint it can provide vital evidence. For
example, in August 1951, a woman's body was found in a rural sport
near Nottingham. The victim, Mable Tattershaw, a 48 year old
housewife, had been strangled. Minute inspection of her clothing
revealed some hairs which were immediately sent to the forensic
laboratory, where microscope examination showed them to be identical
with the head hair of Leonard Mills, an 18 year old clerk and the
chief suspect. Together with other damning evidence, these hairs
helped to take a murderer to the scaffold.
Cloth fibres are often found at the scene of the
crime or on a suspect. In some cases, a small piece of cloth may be
found. The police may even find a matching piece of cloth whose torn
edge will fit the torn edge of the first piece. Such a match is
called a jigsaw fit. Most cloth is made of fibres woven or
intertwined in some way. The kind of fibre and the way in which it
is intertwined determine the character of the resulting cloth.
More often, the police have only tiny fibres with which to work.
It is surprising how often such fibres are left behind, or picked
up, by the criminal. A sweater will shed its own fibres easily and
hold foreign fibres deposited by contact. Even a closely woven
garment, rubbing against a door jamb will leave a few fibre
fragments. A car striking a pedestrian is likely to pick up tiny
fragments of the victim's clothing, even if only a smooth part of
the car comes into contact with the person. These fibres can be
removed from the car by applying sticking tape to the surface,
pulling the tape away, and the removing the fibres from the tape
with liquid.
What is hair used for?
Unless it is burnt, hair is extremely durable. It remains
identifiable on bodies in an advanced state of decomposition or
attached to a murder weapon long after the crime is committed. Hair
is composed of protein substances, chiefly keratin, and head hair
grows at an average weekly rate of about 2.5mm, the beard growing
faster and body hair more slowly. Growth ceases at death, but as the
skin shrinks the hair, especially the beard, becomes more prominent,
giving rise to the murder myth that hair grows after death. The
absorbent property of hair makes its examination important in cases
of arsenic poisoning. Hair picks up the poisons from the
bloodstream, and it is possible to work out the approximate strength
and frequency of the dosage by analysis.
Hair can be used in helping to reconstruct events. Collection of
hair and fibres can indicating contact with surfaces or individuals
and so where individuals have been. Examination of the root
structure can indicate whether hair has fallen out or been
forcefully removed, indicating a struggle.
These days hair can also be used to assist identification through
DNA
analysis. If some root structure is present standard DNA
profiling can be used. Even if you only have the shaft,
mitochondrial DNA testing can be tried.
What are Fibres?
Fibres are the basic unit of raw material in
textile production having suitable length,
pliability, and strength for conversion into yarns and fabrics. A
fibre of extreme length is a filament. Fibres can occur naturally or
can be produced artificially. Fibres also cover some structural
materials as in asbestos fibres (rare these days) and glass
fibres.
Not long ago, most fabrics were
made of wool, cotton, linen or silk. It was easy to identify them
just be feeling and looking. Today a wide variety of synthetic
fibers has appeared on the market, and manufacturers have learn how
to combine many fibers in making a single fabric, making it
difficult to analyse completely or identify all fabrics. However,
there are some simple tests which help greatly in distinguishing
fabrics, the most common being the burning test and chemical
tests.
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Cotton
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Viscose
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Wool
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Triacetate
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Fibres and Hair
Examination of hair and fibres from a crime scene or suspect can yield
a wealth of information.
Hair and fibres can be used in helping to reconstruct events.
Collection of hair and fibres can indicating contact with surfaces or
individuals and so where individuals have been. Examination of the root
structure of hair can indicate whether hair has fallen out or been
forcefully removed, indicating a struggle. All these indicators can be
used to corroborate or refute a persons version of events or act as the
silent witness to a crime.
These days hair may be used to help identify individuals through DNA
analysis. However traditional methods of hair examination are still
used for identification as DNA analysis will not always yield results.
Collecting Hair and Fibres
Generally carried out by applying clear tape to a surface and seeing
what comes off. An item to be examined will be worked over systematically
in a grid fashion. Examiners will use tape of various stickiness depending
upon the surface being examined. Stickier tapes are more efficient at
recovering fibres but may also bury "target" fibres in a
dense mass of background fibres from the surface.
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Identifying Fibres
The first step in identifying a fibre is to
determine its type. Not long ago, most fabrics were made of wool,
cotton, linen or silk. It was easy to identify them just be feeling
and looking. Today a wide variety of synthetic fibres has appeared
on the market, and manufacturers have learn how to combine many
fibres in making a single fabric, making it difficult to analyse completely or identify all fabrics.
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| Cotton |
Wool |
Linen |
Nylon |
Silk |
Rayon |
Most natural fibres such as wool, cotton, and
linen, have distinctive appearances that can be detected under the
microscope. Wool, for example, being an animal hair, has a pattern
of surface scales (although wool that is re-used may have lost there
surface scales in the processing). Silk and most synthetic fibres,
which are produced by the drawing out and solidifying of a liquid,
have smooth surfaces. This characteristics makes them difficult to
distinguish one from another merely by looking at them through the
microscope in normal light.
A synthetic fibre that cannot easily be identified
with the microscope can be subjected to a newer technique, called
infrared spectrophotometry. This process takes advantage of
the fact that all compounds absorb characteristic wavelengths of
radiation. For example (to consider only visible radiation), a leaf
looks green because it contains chlorophyll, a chemical that absorbs
light mainly from the red and blue end of the visible spectrum, but
reflects light mainly in the yellow and green wavelengths.
A scientist can identify a substance, or find our
what compounds it contains, by looking at the way it absorbs light.
If a beam of light containing all wavelengths is passed through the
substance, and the emerging light is spectrum will appear dim and in
other places bright. This variation indicates parts of the spectrum
that suffer the most absorption that is those that are the dimmest
are called the substance's absorption bands. For a specific
chemical substance, the pattern of absorption bands is, in some
cases, unique. It serves as a kind of "signature" for that
substance. This "signature" can be detected and recorded by a
machine called a spectrophotometer.
Besides absorbing visible light, compounds will
also absorb invisible wavelengths, such as ultraviolet or infrared
rays. These are the wavelengths just beyond the blue and the red
ends (respectively) of the visible spectrum. Because the infrared
band extends over a much wider range of wavelengths that does the
ultraviolet or the visible band, it will provide a more complete
signature for the substance.
When analysing a substance by infrared
spectrophotometry, the forensic scientist first mixes it with dry
salt (sodium chloride) and forms it into a disk. Salt is used
because it is transparent to infrared rays. He then focuses infrared
light onto the disk. The light emerges from the disk minus those
wavelengths that have been absorbed by chemicals present in the
sample. The emerging rays are broken into a spectrum by a prism of
rock salt. The light intensities in this spectrum are then measured
and plotted electronically by the spectrophotometer. The machine
produces a graph of peaks and troughs. The pattern of the graph
corresponds to the pattern of absorption bands. By referring to
known signatures for various compounds and comparing these with the
signature produced by the sample, the scientist can tell which
compounds the sample contains. He can also tell from the graph how
much of a compound is contained in the sample and can thus identify,
for example, the origin of fibres.
If a sample of fabric is available a forensic
scientist might look at the construction of the fabric to help trace
it back to a particular type of clothing or particular weave
patterns in the fabric might help in the search for evidence. Some
common weaving patterns are shown at the right.
The edges and shape of a piece of cloth might also
be examined to help in making a physical fit with clothing or fabric
from a crime scene, victim or suspect.
There are also some simple tests which help greatly in
distinguishing fabrics, the most common being the burning test and
chemical tests.
Clues from Hair
These days hair may be used to help identify individuals through DNA
analysis. Traditional methods of hair analysis are still used as
hair evidence will not always allow DNA analysis or the DNA analysis
may be inconclusive or even not useful.
Some preliminary examination of the hair may also help in
determining the value and direction of the DNA analysis. If physical
analysis tells you the hair has no root material attached than DNA
analysis will probably not be helpful. If it tells you have dog
hair it is no use testing a suspect, though it might be worth
testing his dog!
Microscope examination of hair can determine the following
information:
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- Whether it is human or animal
- If human, which race
- Whether it fell out or was pulled
- If animal, which species
- The part of the body it came from
- How it was cut or dressed
| human
head hair |
cat |
dog |
mouse |
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© Jeannette Jolley and Blake Education,
Forensic Science for
High Schools
Book 1,
2000 |
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How do
they do this?
When it is sent for examination to the Forensic
Science Laboratory hair is normally dry mounted on a glass
slide for viewing under a comparison microscope.
To examine it in cross section, the specimen is
mounted in a wax block from which wafer-thin slices are cut and
mounted on glass slides. The cross-sectioned shape and appearance of
the medulla is then viewed microscopically. Impressions of the
cuticular scales are sometimes made on cellulose acetate for
detailed study. The forensic scientist also has a variety of tests
available for dealing with dyed hair and examining for age.
The brilliance of the forensic laboratory cannot
shine, however, without the most thorough and painstaking work of
investigating officers at the scene of the crime: fortunately, in
regard to hair nature is on the side of the crime investigator. The
hair of every part of the body has a definite period of growth and
is continuously lost and replaced: minute examination of clothing
and other articles can therefore pay dividends. Identification
cannot be made with certainty on hair evidence alone. Hair may also
be treated or dressed to alter its natural appearance. This may help
or confuse identification. The best the scientist can do is to say
that a suspect's hair matches a crime sample. This can prove
valuable corroborating evidence of guilt as numerous murder cases
have shown.
Decomposed remains
Evidence provided by hair has played an important
part in a number of murder investigations. In October 1942, the
badly decomposed remains of a woman's body were found buried on a
heath near Godalming, Surrey. It was estimated that the body had
been lying in the heather for about five weeks. This was the so
called "Wigwam" murder, in which the victim, who had been stabbed
and beaten about the head, lived in a crude shelter made of branches
and heather.
Police searching the heath land made several
discoveries which enabled them to confirm the victim's identity as
Joan Peale Wolfe. They also found a heavy birch branch with hair
adhering to it lying in long grass about 400 yards from the body.
Laboratory examination identified this as the weapon responsible for
the head injuries; nine head hairs sticking to the heavy end of the
branch proved to be identical with the head hair of the victim.
August Sangreat, a French Canadian solider from a nearby camp, had
been living with the girl in the "Wigwam" for several months. He was
tried for murder found guilty and executed at Wandsworth
- cuticle;
- The outermost layer or sheath of the hair of mammals.
- The strip of hardened skin at the base and sides of a
fingernail or toenail.
- cortex;
- Anatomy.
- The outer layer of an internal organ or body
structure, as of the kidney or adrenal gland.
- The main layer of the hair of mammals.
- infrared;
- Of or relating to the range of invisible radiation
wavelengths from about 750 nanometers, just longer than red in
the visible spectrum, to 1 millimetre, on the border of the
microwave region.
- Generating, using, or sensitive to infrared radiation
- keratin; A tough, insoluble protein substance that is the
chief structural constituent of hair, nails, horns, and hooves.
- medulla; The inner core of certain organs or body structures,
such as the marrow of bone or centre of hair.
- spectrophotometer; An instrument used to determine the
intensity of various wavelengths in a spectrum of light.
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