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

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 in 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