trace evidence hair and fiber samples. trace evidence trace evidence is circumstantial evidence it...

Trace Evidence

Hair and Fiber Samples

Trace Evidence

• Trace evidence is circumstantial evidence• It will not point to just one person• It can show a certain person was in a certain

place.• People have been found guilty just on

circumstantial evidence.

Forensic Examination of Hair

• Hair falls from the body every day• Unless skin is attached to it, it is hard to use

DNA to say whose it is.• Usually, hair is removed by force at a crime

scene.

Morphology of Hair

• Hair is made from skin cells• Hair has 3 parts – the cuticle, the cortex, and

the medulla1) Cuticle• Hair resists decomposition• Corpses have been dug up with full heads of

hair.• It retains its structure for a long time.

Morphology of Hair

• Cuticle = a scale structure covering the outside of the hair.

• Made of overlapping scales that point toward the tip of the hair.

• The skin that makes of the cuticle are covered in a protein called keratin.

• Finger and toe nails are also skin cells covered with keratin.

Morphology of Hair

• 3 basic patterns to cuticles• Coronal, spinous, and imbricate (page 413)• We use these when matching samples• Looking at the scale pattern tells us if it is

human or animal.2) Cortex• This is the main body of the shaft.• Looks like blocks stacked end to end.

Morphology of Hair

• This is where the pigments for color are found.• How the pigments are shaped and distributed

gives us points for comparison.3) Medulla• It is a collection of cells running up the center

of the hair.• In animals, it makes up ½ the width of the hair.• For humans, it is generally 1/3 or less.

Morphology of Hair

• This percent can change from hair to hair on the same person.

• The medulla can be continuous (uninterrupted), interrupted (with space between), fragmented (no real pattern) or absent.

• Humans usually have fragmented or absent.• Human medullas are shaped like a cylinder.

Morphology of Hair

• A cat’s medulla looks like a string of pearls. (page 416)

• There is a database of the 35 most commonly encountered animals.

3) The root• Root contains what is needed for hair to grow.• The initial growth phase lasts 6 years• When it is pulled from the root, it will have a

follicular tag

Morphology of Hair

• We use the tag for DNA samples• Once the root stops growing, it shrinks.• The hair will last 2-6 months before it falls out.

Identification and Comparison of Hair

1) It tells us if it is animal or human2) Will it match the suspect or victim• We will get samples from the scalp or pubic

regions for comparison.

Factors in Comparison of Hair

• Comparing human hairs has to be done carefully

• We match color, length and diameter, does it have a medulla, and the shape and color intensity of the pigments.

• Dye can be seen in the cuticle• It actually looks like another layer outside of

the cuticle.


• Bleaching hair removes pigments and looks yellow under the microscope.

• If the hair has grown, it is very easy to tell the difference between colored and natural.

• Hair will also collect poison.- This is useful in cause of death.• We use a comparison microscope to look at

hair samples.


• It is easy to tell the differences when they are side by side.

• Because hairs vary on one person, you will need several samples from different parts of the body.

• Human error is the biggest problem is matching samples.

• Once a match is made, it has to be confirmed with DNA.


• It is fairly easy to tell which part of the body the hair came from.

- Use length, medulla type and uniformity.• You can generally tell race from hair, but it is

not 100%.• We cannot tell age from hair.• We can use DNA to figure out the sex.• If hair falls out, there is no root ball attached

to use DNA.

Individualizing Human Hair

• We can find nuclear DNA in the root or on a follicular tab.

• The follicular tab is the best place to find nuclear DNA.

• Getting hair roots for DNA is easier while the hair is in the growth phase.

• Unfortunately, most hair at a crime scene is hair that fell out, not pulled.


• The exception is for violent crimes.• If hairs have fallen out, we can use

mitochondrial DNA.• This is DNA that is passed from the mother to

the child.- Nuclear DNA has parts from both mother and

father.• Mitochondrial DNA is easier to use because

there are more copies.


• This means you can use a 1-2cm length to get DNA.

• But if people are related, you cannot use this type of DNA.

Collection and Preservation ofHair Evidence

• If you have a suspect hair, you need standard/reference hairs for comparison. (Controls)

• Get these from the victim and other people at the crime scene.

• You have to know what part of the body the hair came from to get the right correct reference hairs.

Collection and Preservation ofHair Evidence

• Hair from a crime scene usually comes from the head or pubic regions.

• For the head, you need 50 reference samples• For the pubic regions, you need 25 reference

samples.• You need the full length of hair for

comparison.• Have to pull the hair or clip it at the scalp.

Forensic examination of Fibers

• Just like hair, fiber is left behind at a crime scene.

• It is especially important in cases that involve personal contact.

- Homicide, assault, rape• Fibers can be left behind in a hit and run or in

screens or glass during a break in.• Since we cannot connect fibers to one person.

It is circumstantial evidence.

Types of Fibers

• We used to use only natural fibers• Starting in 1920, we started creating

manufactured fibers.- rayon, nylon, spandex, polyester, etc.• Fibers come from clothing, carpeting, drapes,

wigs, artificial turf, etcNatural Fibers• Made entirely from animal and plant sources

Types of Fibers

Animal fibers• Wool (sheep), mohair, cashmere (goats), fur

fibers (mink, beaver, etc.) and others• We use the same procedures as with human

hair when identifying animal fibers• We still need reference samples to compare

with

Types of Fibers

Plant fibers• The most common plant fiber is cotton• Since white cotton is used so much, it is hard

to match to a person.• The combination of colors in cotton makes it a

little easier.Manufactured fibers• Rayon was created in 1911 and Nylon in 1939

Types of Fibers

• Originally they were created by regenerated fibers.

• These were made from raw materials made from cotton or wood pulp

• This is treated chemically, dissolved, and forced through holes in a spinning jet to make fibers.

• Today they are made from synthetic fibers.

Types of Fibers

• Polymers = long chains of molecules put together from smaller units.

• 1939 – nylon created by accident• A glass rod was put in a beaker and pulled out

a strand that hardened when it hit air.• Polymers are the basic chemical substance of

all synthetic fibers• Polymers are also used to make plastic, paint,

adhesives and synthetic rubber.

Types of Fibers

• Matter is made of molecules• Molecule = elements put together to make a

new substance• Ex) H20, C6H12O6

• Most molecules have less than 100 atoms in them.

• Polymers have millions of atoms per molecule• These are called macromolecules

Types of Fibers

• Polymers are made of chains of monomers• Since there are lots of different monomers,

the number of combinations is almost unlimited

• Nature also make polymers• Proteins for animal hairs are polymers• DNA is a polymer• Starch is a polymer – it is chains of sugars put

together.

Identification and Comparisonof Manufactured Fibers

• If you are lucky you can get a piece of torn fabric that you can match with another piece of fabric

• Normally, you only get a strand or two• You look at it under a comparison microscope.• Looking for color and diameter• If these two things do not match, you stop

doing tests.

Identification and Comparisonof Manufactured Fibers

• Other things you look for are stripes within the fiber or pitting in the fiber so you can make it look shiny.

• Since each manufacturer has its own colors, we can match a fiber to a specific manufacturer.

• This can link a fiber to a house or car.

How We Analyze Fibers

1) Chemical composition• We can find its general type (nylon)• We can find a specific type (nylon 6)• Fibers can be separated into 24 different

categories.• People in the textile industry have lots of tests

to determine the class of the fiber• Need lots of fabrics to do these tests.


• Criminalists only get a fiber or two to work with.

2) Bifringence• Polarized light that passes through a fiber will

spilt in two.• The fiber will bend the light (refraction)• Each type of fabric refracts the light differently• You can look at a single fiber without

damaging it.


3) Infrared absorption• Different fibers absorb different amounts of

infrared light.• We can do this while looking at it under a

microscope.• It will not damage the sample so other tests

can be run.

Significance of Fiber Evidence

• We cannot say that a single fiber came from a single source

• Databases exist for carpeting, but that’s it.• New fabrics come onto the clothing market all

the time, no database for clothing.• With the huge amounts of colors and fiber

types, to make the evidence mean something we have to do lots of test.

Significance of Fiber Evidence

• Color, size, shape, how it looks under a microscope, chemical composition, dye type and content.

• Unless it is denim or white cotton, we should be able to match it.

• The more different fibers you can connect to someone, the stronger the evidence is.

Collection and Preservation of Fiber Evidence

• Because trace evidence has become so important, crime scene investigators have to do a better job of finding it.

• It occurs at almost every crime• You really have to look for it.• Clothing is put in to paper bags, each in a

separate bag.• This is so you do not get cross contamination


• Carpets, rugs and bedding are folded so no fibers get out.

• Car seats are covered completely with plastic• Knives are protected to preserve fiber

evidence• Tape is used to pick fibers off of skin• If fibers are loose, they are put in paper, the

paper is folded, and then put into another container.


• Once it gets to the lab, it is a long and tedious process to get through all of the evidence.

• The crime scene investigator can make this easier by only collecting pertinent trace evidence.

• The better the investigator is, the fewer the samples, the quicker the tests can be run.

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