Hairs and Fibers

textile fiber

-the smallest unit of a textile material that has a length many times greater than its diameter

-fibers can occur naturally as plant and animal fibers, but they can also be synthetic, man-made 

evidence types

-biological/physical: DNA, maternal lineage

-direct/indirect: see it happen or make an assumption

-trace evidence: small quantity

-class/individualizing: class is a subgroup, specific is assigned to one person

4 categories of fibers

-animal

-vegetable

-mineral

-man-made (synthetic)

animal fiber

-wool is most common

-only 1% of textile fibers

vegetable fiber

-about 24% of all textile fibers

-cotton 

mineral fibers

rare - only asbestos

man-made (synthetic)

-about 75% of all textile fibers

synthetic/man-made vs. animal & vegetable

synthetic: uniform, variety of shapes, absence of features

animal/vegetable: irregular only, circular to oblong, visible features (cuticle and medulla)

-animal hair gets denser towards the edges

how can fiber aid investigation

-if someone has clothes with the same fibers found at the scene it can connect them to the scene

-vegetable fibers from a different location can determine relocation

how can hair aid in investigation

maternal DNA

similarities in hair and fiber evidence

-class identification

-associative evidence

fiber analysis

-compare shape, dye content, size, chemical composition, and microscopic appearances

-even if fibers are from two separate places can be associated via comparison, that does not mean they derive from the same source

fiber population studies

-relative frequencies of fiber type/color (generic) on particular surfaces

color block studies

-ability of a specific protocol to discriminate between similar fibers (type/color)

target fiber studies

-probability of finding significant numbers of a specific type of fiber by random chance

direct transfer

-fibers may be transferred from a victim to a suspect

-ex.) fibers from victim’s sweater found on a suspect

secondary transfer

-fibers are picked up by victim and then transferred to suspect

-ex.) victim picks up fibers from couch earlier in the day and then transfers to the suspect later

timing is essential

-early collection of fibers is critical

-within 24 hours an estimated 95% of all fibers may have fallen off a victim or been lost from a crime scene

-only fibers not expected to be found at a crime scene are investigated

placing a cloth on a victim…

-can lead to the transfer of unnecessary fibers

weave pattern

how yarns and fibers are woven into textiles or fabrics

5 major types of weave patterns for textiles

-plain

-basket

-satin

-twill

-leno

warp and weft

determines weave pattern

-warp = length wise fiber

-weft = crosswise (transverse fibers)

textile shedding

-most common form of fiber transfer to be encountered is the shedding from a textile

textile

a flexible, flat material made by interlacing yarns

fibers are spun into yarn or threads

individual fibers can be pulled away or shed from fabrics (textiles)

increasing size

fiber → yarn → textile

thread count

-textiles or fabrics also differ in thread count

thread count

-threads per inch

-higher thread count = higher price

animal natural fiber

silk

vegetable natural fibers

-stem

-leaf

-seed (cotton)

as hair cuticle becomes more damaged

more breakage along the outside

dyes can be analyzed with TLC

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

increasing exclusive sets

all human hairs → body area → racial characteristics → color → microscopic characteristics

variations in human hair

-varies enormously even though we’re a relatively young species

-different people’s hair differs in color, length, diameter, and distribution on the body

-some of these factors are influenced by ancestral affinity, or by age

how much hair do we have

-average person has about 100,000, some people have as many as 150,000

-about 1,100 per square cm on a baby’s head

-by age of 25 this falls to about 600

-btw 30 and 50, falls to about 250-300

-each follicle grows about 20 new hairs in a lifetime, each grows for several years, and can reach over a meter long

-each hair falls out eventually, and is replaced by a new one

vellus hairs

-thinner, softer, kind of all over body

-not as featureful, hard to tell apart on people

hair structure (3 main parts)

-cuticle

-cortex

-medulla

cuticle

-outside transparent covering

-made of overlapping scales

-protects hair

cortex

-2nd layer made of keratin and embedded with pigment called melanin

-contains air sacs called cortical fusi

-gives hair color and form/shape

medulla

-innermost layer running down the center of the cortex

-gives hair its flexibility and offers insulation

hair toxicology

-easy to collect and store

-is externally available

-can provide information on the individual’s history of drug use or evidence of poisoning

coronal cuticle

-type of animal cuticle

-layered

spinous cuticle

-type of animal cuticle

-scale looking

imbricate cuticle

-on human hair

-overlapping

medulla patterns

-fragmentary

-interrupted

-continuous

-stacked

human medulla

-fragmentary, interrupted or continuous

-can also be absent

animal medulla

-can be continuous or stacked

medullary index

-determined by measuring the diameter of the medulla and dividing it by the diameter of the hair

-for human hair, medullary index is generally less than 1/3 of the hair’s width

-for animal hair it is usually greater than ½ of the entire hair’s width

MI = width of medulla/width of cortex

cortex

-can lack a medulla

collecting hair

-collect about 30-50 hairs from each region

postmortem root band (PMRB)

-proteomic analysis of descendent scalp hair segments exhibiting a postmortem hair root band

“Casey Anthony defense wants hair evidence out; expert raises questions about dogs” -Orlando Sentinel