Fiber evidence quiz

Cloth

clothing, bed sheets, towels, tablecloths

Upholstery

vehicle seats, furniture

Carpet

floor, walls, or ceiling of buildings and cars

Cordage

rope, string, twine, nets

Structural Material

stuffing for mattress or upholstery, insulation

3 fun Facts

Indigo is one of the earliest used natural fabric dyes, and still very common today - used to dye blue jeans!

Microfibers are the smallest man-made fibers, 100 times more narrow than the width of a human hair.

The oldest clothing item found is a linen dress from Egypt - 5,000 years old!

Until 1939 all fibers were made from

materials found in nature

Under a microscope, dyed natural fibers show

variation in color.

Natural fibers are

Cotton, Silk, Wool, Cashmere, Linen, Bambo

Synthetic fibers are

cheaper than natural fibers. They can also be made to prefer form new and different functions than natural fibers could. 

Fibers made of Plastics:

Nylon, Acrylic, Spandex, and Polyester

Fibers made by chemically altering wood pulp:

Acetate and Rayon/Viscose

Synthetic fibers are made by squeezing melted material through tiny holes of a

spinneret

The shape and color of a synthetic fiber is

consistent throughout the strand.

Forming synthetic fibers with spinnerets is very similar to the play-doh toys that allowed you to push play-doh through holes to make long strands. Just like play-doh, the holes in spinnerets come in different shapes, which give

fibers unique cross-sections

Analysis of a fiber’s cross section is very important for identification! These two fibers look identical

but their cross section demonstrates they are from a different source

Made from Animal Proteins

Wool, Cashmere, and silk

Made from Plants 

Linen, Bamboo, and cotton

Locard Exchange Principle:

when a person or object comes in contact with another person or object, they exchange material, like hairs, fiber, soil, etc. 

Transference

Some textiles shed fibers very readily (fuzzy wool sweater) while some textiles barely shed fibers at all (windbreaker jacket).

Persistence

Some surfaces readily hold onto transferred fibers while other surfaces do not. Fibers can more easily blow/fall off of smooth surfaces (floors, even smooth fabrics, skin). Rain/water can wash away fibers. Transferred fibers eventually fall off over time, so the longer it has been since the transfer the fewer fibers will be found. 

Fibers are considered

CLASS EVIDENCE

Cross transfer of fibers:

fibers from the victim found on the suspect + fibers from suspect found on the victim. 

Rare or unique fibers

can help narrow the possible source - unique due to low number of items made, or unique due to age/wear

Matching fibers found multiple locations

 in multiple locations can show the path a suspect took, or link to a serial criminal (multiple robberies, etc)

Matching fibers found on multiple victims:

multiple victims: shows a pattern, serial killer 

1. Polyester

2. cotton

3. rayon & acetate

4. Nylon

5. wool

6. other

Most common to least

1. 52%

2. 24%

3. 6%

4. 5%

5. 1%

6. 12%

Fiber evidence collection

Items that may contain fibers are collected to be analyzed in the lab. Items are folded carefully and placed into individual bags.

Once at the lab, items are hung up and scraped so that any loose fibers drop onto a large white piece of paper below for collection.

Tape used to lift fibers from a victim’s skin or objects that can not be collected (furniture, floor).

Individual fibers found at a scene are placed into paper bindles for safe transport to the crime lab.

Some fibers glow under black light, making them easier to find.

Fiber Evidence Comparison

Fibers collected from the crime scene are compared to the possible source of the fibers.

For example, you find one pink fiber at the crime scene. 

Your prime suspect was seen wearing a pink sweater that day!

A known fiber sample is collected from the suspect’s sweater.

A series of tests are used to compare the known fibers to the unknown crime scene fibers to determine if they have similar or dissimilar characteristics.. 

Microscopic Observations

Look at the fiber under the microscope. Compare fibers’ color, shape, size, cross section, etc.

Forensic Fiber Analysis use a comparison microscope to examine both the known and unknown hairs at the same time.

Flame Test:

Compare how the fibers react when on fire. How does the fire behave? How much smoke, what is its color? How does it smell? After the flame is out, what does the ash feel like? 

Chemical Composition

Fiber Analysts can determine the exact chemical composition of a fiber and the colored dye in the fiber using gas chromatography-mass spectrometry (GC-MS). GC-MS first burns/vaporizes the fiber sample, breaking it into individual chemical components. The fiber (now a gas) is sent through the GC-MS machine, which separates and identifies the different chemicals based on size and polarity.

Chemical Reaction

Analysts subject fiber samples to various solvents (strong acids, strong bases etc) and observe how they react (Bubbles? Color change? Does the fiber dissolve?)

Water Retention

Some fibers hold water very well, while others are hydrophobic. To test for water retention, analysts saturate fibers, then spin it in a centrifuge to get out as much water as possible. They weigh the damp fibers, then allow it to dry completely before weighing again. The water retention value is the difference in weight between damp and dry - demonstrating the amount of water the sample retained after centrifuge.

Fluorescence in UV Light

Some fibers glow under UV light (black light). This may be due to the fiber’s own physical structure or because of dyes and other chemicals added to the fiber.

Non-Destructive Tests

Microscopic observation, water retention, fluorescence

Destructive Tests

Flame test, Chemical composition, chemical reaction

These tests are subjective. The data is not measurable, but qualitative, based on the qualities of the fibers. These qualities are determined by (and often subject to!) the opinions of the forensic analyst. 

(Microscopic observation chemical reaction flame test and fluorescence

These tests are objective. The data is  measurable and quantitative. The test provides an exact measurement/quantity/number which is the same no matter who takes the measurement. 

Water retention and chemical composition

Natural fibers can be made from all of these EXCEPT...*

animal proteins

recycled plastic

plant material

fur

recycled plastic

Synthetic fibers are made by

melting material and squeezing it through tiny holes

rolling material out into a flat sheet, the cutting it into thin fiber strips

molding a large, thick strand and then pulling it until the strand is thin

blowing hot air into melted material which causes it to puff up into thin fiber strands

melting material and squeezing it through tiny holes

Which of these are both synthetic fibers?*

wool and nylon

cotton and wool

polyester and linen

nylon and polyester

nylon and polyester

Which of these is NOT true

natural fibers are still more common today than synthetic fibers

insects must die in the process of making silk

rayon is made of chemically altered wood pulp

synthetic fibers are very consistent in color and shape through the whole strand

natural fibers are still more common today than synthetic fibers

Your suspect has a limited edition purple sweater. Only 100 of these sweaters were ever made. A fiber with identical characteristics to the purple sweater was found at a crime scene. Which of these statements is TRUE?

finding this fiber at the crime scene means that the suspect is guilty

the crime scene fiber is not helpful evidence

the crime scene fiber is individual evidence

the crime scene fiber is class evidence

the crime scene fiber is class evidence

You are in charge of training a new CSI. You watch him do the following things - which of these is incorrect?*

before entering the scene, he puts on a full body suit, glasses, foot covers, gloves, and a mask

he finds two white rags on the floor, carefully folds them and puts them in the same evidence bag

he uses a blacklight and finds a fluorescent fiber on the rug

he places the fluorescent fiber into a paper bindle to be brought to the lab

he finds two white rags on the floor, carefully folds them and puts them in the same evidence bag

You have performed four tests on a crime scene fiber and known sample. The fibers have identical characteristics for all four tests. Then, you look at the cross section for each, which looks like the photo below. What can you conclude?*

1/1

the crime scene fiber came from the same source as the known fiber

the crime scene fiber may have come from the same source as the known fiber

the crime scene fiber did not come from the same source as the known fiber

more tests are needed in order to make a conclusion

the crime scene fiber did not come from the same source as the known fiber

You found a single fiber at the crime scene that you want to compare with the known suspect fibers. Which of these tests would you do LAST?

water retention test

chemical composition test

microscope observation

test for fluorescence

chemical composition test

Forensic scientists can use a special machine to determine the exact chemical composition of a fiber. This data is...

subjective, depends on the scientist's opinion of the fiber's characteristics

qualitative, depends on the scientist's opinion of the qualities of the fiber

objective, the data is a fact

may not hold up in court

objective, the data is a fact

Bias is the tendency of someones own feelings swaying his or her opinion. If an investigator believes the suspect is guilty, his bias may cause him to say a fiber from the crime scene matches the suspect when he is looking at...*

the chemical composition of the fibers

comparing the fibers under the microscope

the water retention proprieties of the fibers

comparing the fibers under the microscope