Forensic Fiber Analysis

SFS1. Students will recognize and classify various types of evidence in relation to the definition and scope of Forensic Science b. Distinguish and categorize physical and trace

evidence (e.g. … fibers)

SFS2. Students will use various scientific techniques to analyze physical and trace evidence. b. Analyze the morphology and types of fibers.

ESSENTIAL QUESTIONS

1. How can you distinguish between a natural and manufactured fiber?

2. How can you distinguish between animal and plant-derived fibers OR artificial and synthetic fibers?

3. What factors can affect the transfer of fibers?

ESSENTIAL QUESTIONS

4. What important considerations affect the significance of fiber evidence?

5. What techniques are used in forensic fiber analysis?

What is a fiber? A fiber is the smallest

unit of a textile material that has a length many times greater than its diameter.

A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric.

What is a fiber?Fibers can be categorized as one of two types:◦Natural—derived entirely from plant or animal sources.

◦Manufactured—made from long chains of molecules called polymers

Plant–Derived FibersFlax – oldest cultivated (linen)

Cotton – most prevalentJute – 2nd most important (burlap)

Sisal – used for twine and rope

Hemp – source of 1st paper

Bamboo – cellulose fiber

Flax

Cotton

Jute and Sisal

Hemp and Bamboo

Animal–Derived FibersSilk – derived from silkworm or spider

Sinew – animal tendonWool – sheepOther hair – cashmere

(goat), mohair (goat), angora (rabbit), alpaca, camel, and qiviut (muskox)

Fur – whole pelt

Silk

Sinew

Wool

Cashmere and Mohair

Angora and other hair

Camel

Alpaca

Qiviut

Manufactured Fibers More than half of all

fibers used in the production of textile materials are man-made.

Some man-made fibers originate from natural materials such as cotton or wood (artificial); others originate from chemicals (synthetic).

Synthetic Fibers Rayon –1st artificial fiber

from wood Acetate – artificial from wood

(satin) Nylon –1st synthetic fiber Olefin – synthetic (carpet) Acrylic – synthetic wool Polyester – most common

syn. Specialty fibers – Kevlar,

Spandex

Rayon

Acetate

Nylon

Olefin and Acrylic

Polyester

Specialty Fabrics

spandexKevlar

Natural vs. Synthetic

wool other hair silk flax cotton polyester

Fiber Evidence Fibers are gathered at a

crime scene with tweezers, tape, or a vacuum. 

They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. 

Fiber Evidence The problem with fiber evidence

is that fibers are not unique.  Because it is considered class

evidence, it cannot pinpoint an offender in any definitive manner. 

There must be other factors involved, such as evidence that the fibers can corroborate or something unique to the fibers that set them apart.

Fiber EvidenceThe type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers.

A. The number of fibers on the clothing of a victim identified as matching the clothing of a suspect is important in determining actual contact.

◦ The greater the number of fibers, the more likely that contact actually occurred between these individuals.

Important Considerations

Important ConsiderationsB. The length of time between the

actual physical contact and the collection of clothing items from the suspect or victim is also important.

◦ If the victim is immobile, very little fiber loss will take place, whereas the suspect's clothing will lose transferred fibers quickly.

◦ The likelihood of finding transferred fibers on the clothing of the suspect a day after the alleged contact may be remote, depending on the subsequent use or handling of that clothing.

C. The location of fibers on different areas of the body or on specific items at the crime scene influences the significance of the fiber association.

D. The identification of less common plant or animal fibers at a crime scene or on the clothing of a suspect or victim would have increased significance.

Important Considerations

E. The amount of production of a particular man-made fiber and its end use influence the degree of rarity of a given fiber.

F. Unusual cross sections (often manufacturer-specific) encountered through examination can add increased significance to a fiber association.

Important Considerations

Generally, the analyst gets only a limited number of fibers to work with—sometimes only one.

Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home.

Fiber Evidence

1. Fibers should be first examined using stereomicroscopy.

Physical features such as crimp, length, color, relative diameter, luster, apparent cross section, damage, and adhering debris should be noted. Fibers are then tentatively classified into broad groups such as manufactured, natural, or inorganic. If the sample contains yarns, threads, or sections of fabric, construction should be recorded.

Steps of Fiber Analysis

2. If all of the characteristics are the same under the stereoscope, the next step is to examine the fibers with a comparison microscope to discriminate between fibers, especially those that appear to be similar.

Steps of Fiber Analysis

3. Dyes are analyzed using different techniques

Microspectrophotometry (MSP)

Steps of Fiber Analysis

Light absorbed by or reflected from a sample is separated into its component wavelengths, and intensity at each wavelength plotted.Can be IR or UV/Vis

Thin-layer chromatography (TLC)

Steps of Fiber Analysis

Dye components are separated by their differential migration caused by a mobile phase flowing through a porous, adsorptive medium.

4. The chemical makeup of the fiber itself can be examined using

Gas chromatography –Mass spectroscopy (GCMS)

Steps of Fiber Analysis

The GCMS instrument is made up of two parts. The gas chromatography (GC) portion separates the chemical mixture into pulses of pure chemicals and the mass spectrometer (MS) identifies and quantifies the chemicals.

Other Fiber Analyses Burning the fiber

◦Odor of burning hair – Animal source◦Odor of burning paper – Plant source◦Melts, but does not burn – Manufactured

Chemically treating the fiber◦Dissolves in strong acid – plant, silk, or manuf.

◦Dissolves in strong base – wool