Download PenChromatograms

Hair Analysis
Besides the color of hair, there are a lot of other characteristics of human hair that can be looked
at. Some hair is flat when observed under a magnifying glass and some is round. Some hair is finer and some
hair is courser. Round hair tends to be straighter than oblong hair. Flat hair tends to be kinky. The forensic
scientist must also be able to tell the difference between animal fur and human hair, even if the piece of material
the forensic scientist has to work with is very, very small. Cat hair is usually finer than human hair or dog hair.
Dog hair can be of two different kinds. The outer coat is generally very course and often straight. The undercoat
is often fine and can be very curly.
In human hair, the color of the hair can make a difference too. Generally speaking, dark hair is
thicker than blond hair and red hair is the finest. But then hair that has been colored artificially can give false
clues. Hair is composed of two basic layers. The inner layer contains the pigment(s). Melanin is the most
common pigment in hair. The amount of melanin determines the color of the hair. The more pigment, the darker
the hair. Some hair is white. It generally has bubbles in the inner layer.
Today when the investigator finds a piece of hair at the crime scene, he/she will send it to the lab
for DNA analysis. There are two types of DNA analysis that can be done. We will be looking at one of them
later. This method analyzes the DNA that is in the nucleus of the cell. It directs most of the cell functions. Cells
of higher order animals have another structure in them called mitochondria. The exact origin of mitochondria is
unknown. Some think that some cells incorporated bacteria into them millions of years ago and changed the
bacteria to benefit the cell. The new structures were replicated when the cell replicated and were passed on.
Eventually they became a vital part of the cell. The main difference between nucleus DNA and mitochondria
DNA is that half of the nucleus DNA came from each parent, but all of the mitochondria DNA comes from the
mother. This makes tracing lineage easier through the mother. The hair must have living cells from the root
attached to it if regular nucleus DNA tests are to be run, but if mitochondria DNA is to be tested, there is no such
requirement. Therefore any piece of hair can be tested. This is the most popular test that is done on hair today in a
real crime scene.
We are going to be kept to the old fashion methods of looking at hair because of a lack of
equipment. We will be looking at the hair under a microscope to determine if it is likely from a dog, cat, or
human. We will also be looking at the basic shape, curliness, and size of the hair if it is from a human. We will be
looking at color also, and whether or not the hair is dyed
Hair Structure and Life Cycle
Structure of Hair
Hair is composed of strong structural protein called keratin. This is the same kind of protein that makes up the
nails and the outer layer of skin.
Each strand of hair consists of three layers.
1) An innermost layer or medulla which is only present in large thick hairs.
2) The middle layer known as the cortex. The cortex provides strength and both the color and the texture of hair.
3) The outermost layer is known as the cuticile. The cuticle is thin and colorless and serves as a protector of the
cortex.
Structure of the hair root
Below the surface of the skin is the hair root, which is enclosed within a hair follicle. At the base of the hair
follicle is the dermal papilla. The dermal papilla is feed by the bloodstream which carries nourishment to produce
new hair. The dermal papilla is a structure very important to hairgrowth because it contains receptors for male
hormones and androgens. Androgens regulate hairgrowth and in scalp hair Androgens ma cause the hair follicle
to get progressively smaller and the hairs to become finer in individuals who are genetically predisposed to this
type of hair loss.
Parts of a hair
The diagram on the right shows the parts of a human hair. A hair develops from the cells of the hair bulb. These
cells move up to form the root and then the shaft of the hair. The diagram on the left shows the three layers of
dead cells that make up a hair
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 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:
*
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
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.
Some pictures of different hairs and fibres under magnification.
What is hair used for?
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.
Human hairs are generally consistent in color and pigmentation throughout the length of the hair shaft, whereas
animal hairs may exhibit radical color changes in a short distance called banding. The distribution and density of
pigment in animal hairs can also be identifiable features. The pigmentation of human hairs is evenly distributed,
or slightly more dense toward the cuticle, whereas the pigmentation of animal hairs is more centrally distributed,
although more dense toward the medulla.
The medulla, when present in human hairs, is amorphous in appearance, and the width is generally less than onethird the overall diameter of the hair shaft. The medulla in animal hairs is normally continuous and structured and
generally occupies an area of greater than one-third the overall diameter of the hair shaft.
The root of human hairs is commonly club-shaped, whereas the roots of animal hairs are highly variable between
animals
Bat

The coronal, or crown-like scale pattern, is found in hairs of very fine diameter and resemble a stack of
paper cups. Coronal scales are commonly found in the hairs of small rodents and bats but rarely in human
hairs.
Cat

Diameter: fine; little variation

Medulla: uniserial ladder (fur hairs) continuous; occasionally vacuolated in coarser hairs

Scales: spinous; very prominent

May be banded

Root: elongated, no distinct shape; fibrils frayed at base of root
Dog

Diameter: fine to coarse (usually coarser than cat hairs); diameter may vary to give short hairs a barrellike appearance

Medulla: continuous, vacuolated to amorphous, occasionally very broad

Scales: generally not prominent

Unbanded: pigment occasionally very coarse and extending into root

Root: spade-shaped
Horse

Diameter: very coarse

Medulla: absent to unbroken; cellular or amorphous (mosaic pattern)

Scales: imbricate; without protrusions from hair shaft

Characteristic color; pigment fine, evenly distributed; few ovoid structures

Root: area adjacent to root tapers to bulb-shaped root
Hair Worksheet
Hair
Cat
Dog 1
Dog 2
Horse 1
Horse 2
Bat
Human 1
Human 2
Human 3
Animal?
Color?
Shape?
Size?
Dyed?
Cuticle observations
Human 4
Human 5
Unknown 1
Unknown 2
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric4.htm
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric1.htm
http://www.iamaweb.com/Animal_Hair/animal_hair_images.html
http://www.bergen.org/EST/Year5/HairAnalysis.htm
http://www.fbi.gov/hq/lab/fsc/backissu/jan2004/research/2004_01_research01b.htm
http://www.fbi.gov/hq/lab/fsc/backissu/july2004/research/2004_03_research02.htm
Fibers
Wool is the most commonly used animal fiber. The fiber is obtained from the soft, hairy covering of sheep and
sometimes goats. Under the microscope, the wool fiber looks like a long cylinder with scales on it. The fiber is
very curly and springy. Cloth made from wool includes cashmere, camel's hair, alpaca, covert cloth, flannel,
gabardine, mohair, serge, tweed and worsted.
Silk, another common animal fiber, was once quite popular, but has been replaced to a great extent by such
synthetic fibers as Nylon, Orlon, and Dacron. Silk is made by the mulberry silk worm when spinning its cocoon.
Under the microscope the silk fiber appears as a thin, long, smooth and lustrous cylinder. Cloths made from silk
include brocade, brocatelle, chiffon, crepe, velvet, crepe de Chine, foulard, lame, moiré, satin, taffeta, tulle, and
falle.
Cotton is the most widely used plant fiber. Cotton fibers are the hairs found on the seeds of the cotton plant. If
possible, obtain a cotton boll on its stem. Examined under a microscope, the cotton fibers (use a few strands of
absorbent cotton) will look like a flattened, irregular, twisted ribbon. Many high school chemistry and physical
science textbooks (and books on identifying textiles) have excellent pictures of fibers as seen through a
microscope.
Cloths made from cotton area cheesecloth, organdy, chintz, gingham, crinoline, muslin, percale, calico,
velveteen, seersucker, some poplin, sail cloth and canvas. Most cotton thread has been treated to make it smooth
and lustrous; this is done by stretching the cotton and immersing it in a concentrated solution of cold sodium
hydroxide (lye). Cotton treated in this manner is said to be mercerized.
Another common plant fiber is linen, which comes from the flax plant. This fiber is linen, which comes from the
flax plant. This fiber is long, lustrous, and smooth. Under the microscope it looks like bamboo can, with jointed
cells and split, tapered ends. Point out that linen is often used to make handkerchiefs, tablecloths, napkins,
summer clothing and blouses.
Jute and hemp, other plant fibers, are not as fine as cotton and linen, and are used to make carpet backing rope,
twine and sacks.
Rayon is one of the first successful artificial fibers. It is made from cellulose. When manufactured, the rayon
fibers resemble silk. Under the microscope, the rayon fiber looks like a smooth, lustrous cylinder. Rayon can be
made into cloth that is hard to distinguish from silk, cotton, linen, or wool. Celanese is one form of rayon.
Today there is a wide variety of synthetic fibers; all have trade names such as Nylon, Orlon, Dacron, Vinyon,
Aralac, Acrilan, Velon, Dynel, Banlon and Lycra. Like rayon, these fibres resemble silk, and under the
microscope look like smooth, lustrous cylinders. Synthetic fibers are easily identified because of their uniform
thickness (the thickness of natural fibers varies). Synthetic fibers area made into fabrics that have special
properties..
Glass and asbestos can also be spun into thread and woven into fabrics. Glass fibers are made by stretching
melted glass into fine filaments, which are spun into thread for weaving into cloth. Lightweight glass fibers are
used to make long lasting windows curtains, drapes, and lamp shades. Heavier glass fabrics are used to make
fireproof theater and school curtains.
Asbestos is the name given to a group of minerals that occur naturally as masses of strong, flexible fibers that can
be separated into thin threads and woven to make asbestos cloth. These fibers are not affected by heat or
chemicals and do not conduct electricity. Asbestos cloth was used in fireproof theater curtains and protective
suits for use by fire fighters. It was also used as a building material, brake pads and a range of other products.
It is now know that the fibers of asbestos are a dangerous irritant. Even exposure to small amounts of asbestos
dust can lead to a range of illnesses such as asbestosis, a serious lung inflammation caused by asbestos exposure,
and Mesothelioma a cancer of the chest and abdomen. Although asbestos products are rarely made these days,
they can still be found, particularly in old buildings.
References;
*
Handweavers and Spinners Guild of Victoria Inc
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 analyze completely or identify all fabrics.
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 reused 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 analyzing 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.
What are Fibres?
Fiber
Wool
Silk
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 analyze 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.
Fiber Worksheet
Look at the fibers with a hand lens.
Put a small piece of the fibers into a spot plate. Be sure you mark on a piece of paper what material you
put into which well.
Add a drop of HCl to each fiber. Do you see any difference in the way the fibers react?
Add a drop of I2 to each of the fibers. Any difference?
Add a drop of H2O2 to each of the fibers. Any difference?
Be sure to record your observations.
Try holding a small strand of the fiber with forceps just above the flame of a match or candle. What do you
observe?
Magnifier
HCl
I2
H2O2
Burning
OtherObservations
/Microscope Observations Observations Observations Observations
Observations
Cotton
Linen
Polyester
Nylon
Acrylic
Acetate
Spandex
Fibers Web Resources
http://www.chemheritage.org/EducationalServices/nylon/nylon.html
http://www.tx.ncsu.edu/science_olympiad/Fiber_kits.htm
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric4.htm
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric3.htm#Introduction
http://www.atexinc.com/Virtual_Lab_Assistant_REG_Isis.ppt
http://legacy.ncsu.edu/classes/tms211L001/schedule.htm
omatography
Most things that are colored are mixtures of different substances of various colors. In a mixture you have
several different kinds of chemicals that are all next to each other but not reacting. Since it is just a mixture and
not a compound, the different chemicals can be separated. Since each pen manufacturer, or juice manufacturer, or
indeed each type of grass uses a somewhat different formula to produce its colors, each possesses a unique,
identifiable character. As a matter of fact, the same basic technique is used for identifying all sorts of things
including DNA.
A technique known as chromatography, which is a term taken from the Greek language & means “written
in color”, will be used to separate the substances into their various colors. This is exactly the same technique that
a “real” crime lab would use to determine the manufacturer of the ink used in a note found at the crime scene or
later sent in as a ransom note. It would also be used on any stains or juices found at the scene, etc.
To separate the substance into it’s components a piece of filter paper, that has a similar composition to
that used in most coffee filters is used. Sometimes the paper is a wide strip of paper, sometimes it is a long strip.
You may do it either way. If you have a lot of different substances to test, the wide one is often most convenient.
If you only need to test a couple, it is often just as easy to use the long ones. Of course it depends on what is
available in the lab. To give you some knowledge on how to handle both kinds, we will try both. Regardless of
the type of paper used, the idea is to put a fairly small dot of the substance to be tested about 1.5 cm up from one
edge of the paper. The bottom of the paper is then dipped into a liquid of some sort, such that the liquid level is
below the level of the dot. The liquid is chosen such that it will dissolve the substances that make up the color.
The liquid will travel up the paper, dissolve the colors, and drag them along as the liquid continues to travel up
the paper. Since the molecules making up the colors are of different sizes and hence different weights and
different dissolving properties, they will migrate up the paper at different rates. This will then separate them into
their various components. These signature chromatograms can then be compared against knowns to determine
what the unknown is.
We will only be trying a couple kinds of chromatograms that use water as the liquid to dissolve the
substances and separate them into their component parts. We will leave some of the more exotic separations for
you to experience later.
PenChromatograms
1.Take a wide rectangular piece of filter paper and use a pencil to draw a line about 1.5 cm from the
bottom edge of 1 long side.
1.5 cm
2. Place small dots of each of the known materials you are to test spaced about 1 cm apart along the line
you just drew. Be sure to label what the dots are on the paper ABOVE the dot.
3. Roll the paper up like a cylinder & staple the ends together.
staples
4. Put about 1 cm of water in a Petrie dish.
5. Set your chromatography paper in the dish with the dot side down. Be sure the water level in the Petrie
dish does not touch any of the dots on the line you made.
6. While that chromatogram is developing do the same thing over for the knowns of another set of
materials.
7. Take 2 strips of chromatogram paper and make a line about 1.5 cm from the bottom with a pencil on
each.
1.5 cm
8. Bring your prepared pieces of chromatogram paper to the instructor who will
place a dot on the papers as your unknowns.
9. Hang the papers in a beaker by placing a wooden stick through the hole in the top & resting the wooden
stick on the lip of the beaker.
10. Use your wash bottle to put enough water in the beaker so that the bottom of the chromatograph paper
just is in the water, but not so much that the dots are in the water. Be sure that you do not get any water on
the chromatography paper as you are putting it in.
11. The chromatograms are done when the water level gets up to about 1.5 cm from the top.
12. Take the chromatograms out and spread them on a paper towel to dry.
13. Which of the knowns do your “crime scene” chromatograms match up to?
Juice Chromatograms
Juice Chromatograms are done very much like pen chromatograms except for the method used to put the
material on the paper. In pen chromatograms you can use the pen to place a dot on the paper directly, but
in juice chromatograms it is necessary to use an instrument to place the juice on the chromatography
paper. A toothpick works well for this. Dip the toothpick in the juice and touch it to the chromatography
paper on the line. Do not let too much liquid get on the paper. The dot should be about the size you got
when you did the pen. Use a different toothpick for each of your known juices. You do not want the juices
contaminated. With juices, it is usually necessary to let the liquid from the first dot soak in a bit and then
go back and put a second dot right in the same place as the first dot. You should let the liquid soak in for
15-20 seconds between dots. It is usually best to apply 3-4 dots of juice in the same place to get enough
pigment to make a visible chromatogram. Each juice then should have a different place on the paper.
Paper Chromatography Web Resources
http://www.yesmag.bc.ca/projects/paper_chroma.html
Fingerprints
You have probably heard that everyone has different fingerprints. Even identical twins do not have
exactly the same fingerprints. But there are certain patterns that fingerprints display. There are three levels of
fingerprints. At the first level, the fingerprints are divided up into 3 basic types, and then one type has a couple of
different categories. The first thing we will learn is to identify the different types of fingerprints. Then we will
learn to create finger print impressions. We will then identify our fingerprint types. Then we will take different
fingerprints taken from a crime scene and see if we can identify any of the suspect’s fingerprints as being at the
crime scene.
The 3 basic types of 1st level fingerprints are whorl, loop, and arch. The arch is further broken up into
plain arch and tented arch. The next few diagrams are examples of these types as well as instructions on how to
recognize them. These are all blown up larger than real life so that you can see the differences. This level is used
to sort the fingerprints into manageable groups to further analyze.
Ridges start from both sides
and rise smoothly in the center.
Ridges rise in the
center, pointing upward or forming a triangle.
Think of it as a Road Test. Can you ride your bicycle
across the hill without getting a flat tire from a puncture?
Look for a camping tent in the center of pattern.
Ridges start on one side,
curve and return to the same side.
Look for a river that appears to be flowing into a lake
formation.
Ridges appear to
circle, spin, whorl, or spiral.
Look for a target in the center of the pattern
There's a method of fingerprint classification called the Henry classification. It goes by whorls:
For a whorl on your right index, give yourself 16.
Right ring: 8
Left thumb: 4
Left middle: 2
Left pinky: 1
Add one, and you have your top number, a maximum of 32.
Right thumb: 16
Right middle: 8
Right little: 4
Left index: 2
Left ring: 1
Add one for your bottom number.
So if you have all whorls, you get a 32/32.
If you have, say, a loop, on your left little, but all other whorls, you get 31/32, and so on.
Sixty-five per cent of all fingerprint patterns consist of loops; whorls make up about 30 per cent; and arch
the remaining 5 per cent.
Today computers are used to keep records of fingerprints electronically. This is called the AFIS
(Automated Fingerprint Identification System). These are national standards that are used in all law enforcement
throughout the country. So someone arrested in Indiana can be quickly matched with fingerprints found at a
crime scene anywhere in the country.
One thing that people have often wondered about is what causes the ridge patterns. If the ridge patterns
were determined genetically, then identical twins should have the same fingerprints. If genetics does not cause
the ridge patterns, then what does? Look closely at your fingers. Do you have the same 1st level structure on all
ten of them? Most people do not. If you do, you may need to do this exercise on someone else who does not have
all the same 1st level structure. Look at your fingers from the side with your palms up. Do all of the finger tips
stick up the same amount or do some of your finger tips stick up more than others. Which 1st level patterns are on
the fingers that stick up most? Which 1st level patterns are on the fingers that stick up least? The amount the
fingers stick up is controlled by a layer of fat on the fingers called the volar pads. The 1st level of fingerprint
pattern is controlled by the volar pads.
At the 2nd level the detail of the fingerprints are seen with what are called minutia points. This is the level
that is used to positively identify the fingerprints as belonging to one person or another. Generally courts require
that there be at least 10 definite match points before a positive ID is made. The standard used to be 7 match
points, but two many innocent people were convicted using this standard.
There are about 30 different types of minutia points in the 2nd level structure. These include:
A delta looks something like this:
| |
/ \
/ /\ \
and is basically three sets of ridges meeting each other.
There are also bifurcations:
__
_/
\__
Double bifurcations:
__
_/
__
\___/
\__
Trifurcations:
__
_/__
\__
Islands (short ridges):
___
_/ _ \__
\___/
Ridge endings:
__
_/
\__
___
_
__
\__/
Eyes (enclosures):
__
_/
\__
\__/
Bridges:
______
__/____
Spurs:
______
\_
_
____/__
And last, but not least, dots.
_______
___.____
Fingerprinting
Fingerprints left at a scene can be classified into three types. They can be visible because the fingers that
made them were covered in paint, ink, blood, etc. The fingerprints may be visible because they were made in a
soft material such as putty or clay. Or the prints may not be visible. We call invisible prints latent prints. To be
useful, the prints must be visible and there must be a way or recording the prints. Today that also means getting a
digital record of the print so that it can be compared in the AFIS (Automated Fingerprint Identification System).
Photographs are also an excellent method of obtaining a permanent record of the print. That way the photographs
can be presented as evidence in a court of law.
Obtaining permanent records of the first two types of prints are not a problem. With today’s digital
cameras, it is possible to get both a digital record and a photograph for use in a courtroom at the same time. It is
the third type of fingerprints that are the most difficult to obtain. There are new methods of lifting latent
fingerprints being developed all of the time. The Web Page for fingerprinting gives a link to one of the best
resources I have seen on deciding what type of latent print lifting method to use depending on the surface, the
size of the surface that the print is on, and the value of the surface and whether or not it can be destroyed in the
fingerprint lifting process. The site also gives the chemical basis for the lifting.
Lifting fingerprints is based on the principle that we have sweat glands in the friction ridges of the fingers.
These secrete mostly water, but some body salts and some oils as well. These can attract some types of particles
such as the fine powders used in dusting or Iodine or Superglue. These other particles that are attracted to the
residue left from the fingers can then be photographed.
Tracks-foot and bicycle
The art of figuring out what shoe or bicycle is the art of being able to see mirror images. It is not nearly as easy as
it sounds.The information abounds on these subjects. If you want to read a couple of excellent books on the
subject, I suggest you check out:
McDonald, Peter, Tire Imprint Evidence, CRC Press, 1993 &
Bodziak, William, Footwear Impression Evidence, Elsevier, New York, 1990
Arthur Conan Doyle in the Sherlock Holmes adventure The Adventure of the Priory School in 1901 had Holmes
state there were forty-two (42) different bicycle tire treads then. You can imagine how many more there are
today. It is estimated that a motor vehicle is involved in 75% of the major crimes committed today. But because
most of you do not yet drive a motor vehicle, we will confine our look at tires to bicycle tires. We will be
examining some photographs of tires and impressions to see if we can figure out what tires made what
impressions.
What things should you consider when trying to decide if a particular shoe or bike tire made a particular track? Is
it at all possible that different sized shoes actually have the same bottom? How do you know the picture of the
track and the picture of the shoe or bike tire are blown up the same amount? What can you tell from the depth of
the track? What will happen to the track if the cameral is held at an angle?
Track Web Resources
http://staff.imsa.edu/~brazzle/E2Kcurr/Forensic/Tracks/ShoeLibOld.html
http://staff.imsa.edu/~brazzle/E2Kcurr/Forensic/Tracks/TireLib.html
http://www.talontire.com/glossary.html
http://staff.imsa.edu/~brazzle/E2Kcurr/Forensic/Tracks/ShoeVsHeightIMSA.htm
http://members.aol.com/varfee/mastssite/home.html
Spatter Web Resources
http://www.brazoria-county.com/sheriff/id/blood/index.htm
http://www.bergen.org/EST/Year5/EA/Serology2_1.htm
http://www.bloodspatter.com/BPATutorial.htm
http://www.benecke.com/bloodspatter.html
http://www.physics.carleton.ca/~carter/index.html
http://www.bergen.org/EST/Year5/blood.htm#Spatter
http://www.jfklancerforum.com/sherryg/images/Multi_items.jpg
http://brazoria-county.com/sheriff/id/blood/bloodspatter_general_info.htm
Refraction
When light waves go from one medium to another, if they are not going straight down, they bend. If you
take a glass of water, put a straw in it and look at the glass and straw from the side, it will appear as if the straw
bent. You know it did not, but it appears that way because the light is what did the bending. This is because light
travels faster in air then it does in glass or water. It does not travel the same speed in glass as it does water. If you
take a glass bead and put it into a cup of water, you will still be able to distinguish where the bead is. If you put a
glass bead into a small cup of corn oil, it will almost seem to disappear because the speed of light is very close in
glass and in corn oil.
How much the light bends depends on the difference in the speeds of the light in the different materials.
The relationship is called the Index of Refraction and is governed by Snell’s Law. If you put a solid into a liquid
with the same Index of Refraction, it will appear to disappear.
Glass is not just one thing. In its pure form, it is silicone dioxide. SiO2. But in order to make glass useful
for different purposes, different impurities are deliberately put in. You have undoubtedly heard of leaded glass,
for instance. So glass does not just have one index of refraction. Glass that is used in windows in cars has plastic
imbedded in it to hold the shards together when it breaks so that it does not go flying around cutting people and
getting in people’s eyes. We can therefore use these two pieces of information to determine where glass may
have come from by finding the index of refraction of the glass using liquids with different indexes of refraction.
You will put the glass in different liquids and see if the glass appears to disappear or not. The liquid that
the glass appears to disappear in most has the closest index of refraction.
In a normal crime lab, this would be done with very sharp edged pieces of glass and more liquids then we
will have access to in this event. The technician would be using a stereoscope to determine exactly when the glass
disappeared. We will not have access to this sophisticated equipment, so we will have to do a bit of guessing on
what the exact index of refraction i