Trace Evidence

Patterns in the Cortex

• Coronal (crown-like)

• Spinous (petal-like)

• Imbricate (flattened)

Patterns in the Medulla

• Absent

• Fragmental - - -

• Interrupted - - - -

• Continuous ————-

Process of Hair ID

• distinguish if animal or human

• microscopic examination of morphology

  • abnormalities

  • pattern

  • infections

  • color

• DNA profile

Examination of hair may determine

• body area of origin

• ancestral origin

• age (only infant)

• sex (from DNA)

• forcible removal (sometimes)

• alive or deceased

Collection and Preservation of Hair

• ensure adequate number of reference samples are submitted to lab

  • should come from same area of body (typically head or pubic area)

  • combing of pubic area should occur before samples are taken

• hair pulled from skin or cut at skin level

Natural Fibers

• cellulose based

• protein based

• mineral based

Manmade Fibers

• natural polymer-based

• synthetic polymer-based

• mineral and specialty

Examination of Fibers

• microscopic

  • morphological features

    • color

    • diameter

    • surface qualities

  • computerized spectrophotometry

  • chemical composition

  • infrared absorption

Collection and Preservation of Fibers

• may be overlooked or difficult to see with the naked eye

• items should be individually packaged in paper bags

• large pieces may be folded and/or wrapped in plastic

• small pieces may be collected with forceps and placed in a small piece of paper, which is then folded and placed in another container

Paint

• paint fluid dries on surface to create a hard film

  • pigments

  • additives

  • binders

• paint on automobiles often seen in forensic cases

Examination of Paint

• microscopic examination

• examination of binders

  • pyrolysis gas chromatography

  • infrared spectrophotometry

Collection and Preservation

• take care to keep the paint chip intact

• pick up with tweezers to scoop up with papere

• preserve in druggist fold or glass/plastic vial

• collect reference samples

  • in case of a hit-and-run, collect from undamaged area of vehicle, but close to location of impact

  • in cases of cross transfer between vehicles, samples containing all layers is required

    • use disposable scalepls

    • new scalpel with each sample

Composition of Glass

• hard, brittle, amorphous substance composed of sand mixed with various metal oxides

  • sodium bicarbonate

  • borosilicates

  • tempered glass

  • laminated glass

Sodium Bicarbonate

• sodium, calcium, magnesium, and aluminum

• typical glass in home windows

Borosilicates

heat resistant glass

Tempered Glass

glass stressed through rapid heating and cooling

Laminated Glass

sandwiched by plastic

Examination of Glass

• comparing fragments (puzzle pieces)

• measuring and comparing density of sample and reference

• refractive indexing

  • “immersion method”

  • Becke Line

Classification of Glass

• FBI laboratory’s collection of density and refractive indices of glass

  • frequency of occurrence of use in the US

Glass Fracture Patterns

• radial

• concentric

Direction of Force in Glass Fractures

• stress marks

• craters

Collection and Preservation of Glass

• if able, direction of impact should be determined prior to glass collection

• if possibility of piecing together

  • collect as much glass as possible

• take reference glass

• should be packaged in solid containers to avoid further breakage

• shoes or clothing to be examined should be wrapped in paper for transport

• indicate interior and exterior of glass

Soil

• any disintegrated material, natural and/or artificial, that lies on or near the earth’s surface

  • rocks

  • minerals

  • vegetation

  • animal matter

  • glass

  • paint chips

  • asphalt

  • brick fragments

  • cinders

• value lies in the property of transference

Examination of Soil

• Visual comparison

  • color

  • consistency/texture

• Microscopic examination

  • presence of plant and animal material

  • mineral composition

    • crystals

• use geographic variation in soil

  • soil variation probabilities

Collection and Preservation of Soil

• must establish variation of soil at the scene

  • standard soils should be collected at various intervals within a 100-yard radius of the scene, as well as the site of the crime

• specimens should be representative of the soil removed/carried by the suspect

• samples packaged in individual, labeled containers

• soil on objects should be wrapped in plastic and taken from the scene whole

• lumps of soil should be collected intact