Fibers pgs 59-65 Fibers & cloth fragments offer much greater evidential value because they...

Fiberspgs 59-65

• Fibers & cloth fragments offer much greater evidential value because they incorporate numerous variables:– Number of fibers in each strand, diameter of

strands & fibers, direction & number of twists, type of weave, dye content, presence of any foreign material that may be adhered to fibers or embedded among them

Fiberspgs 59-65

• Fibers may be classified into two broad categories – natural and manufactured.

• Natural fibers – animal (wool, silk, animal hair fibers such as mohair), vegetable (seed fibers such as cotton; bast fibers such as flax, hemp, & jute; leaf fibers including manila), & mineral (asbestos).

Fiberspgs 59-65

• Man-made (manufactured) fibers include natural-polymer fibers (rubber, rayon & cellulose ester), synthetic-polymer fibers (polyvinyl derivatives, polyurethane, & polyester), & other fibers (carbon, glass, metal & ceramic).

• Fibers from hair coverings are identified by their color & structural characteristics under the microscope

Fiberspgs 59-65

• Plant fibers – distinct morphology/structure under microscope makes them easy to ID

• Cotton fibers have a twisted, ribbon-like form. Linen fibers resemble knobby tubes.

• Cotton is the most prevalent of plant fibers. Alone its evidential value is weak, but presence of dye adds a significant measure of distinctiveness.

Fiberspgs 59-65

• For all but the most commonly found natural fibers specialized techniques may be required.

• Maceration is necessary for examining bast & leaf fibers that occur in bundles.

• Man-made fibers generally show fewer identifying features than natural fibers. So several methods of identification are used.

Fiberspgs 59-65

• Infrared spectroscopy – differentiating several types of nylon fibers

• Solubility tests – differentiate between certain other fiber types

• Cross sectioning – cutting in half (perpendicular to long axis)

• Standard microscopic examination used to determine optical properties such as birefringence & refractive indices.

Fiberspgs 59-65

• A fiber’s dye may be analyzed by thin-layer chromatography where dye components soak through an absorbing medium to separate them.

• Criminalists seek to learn type of fiber, natural or man-made; generic type & subtype, color & shade, expected use, manufacturer, period of manufacture, relative commonness or rarity of fiber.

Fiberspgs 59-65

• That transfer of fibers occurs is not just a theory (Locard’s Exchange Principle) but has been established by scientific tests.

• 80% of fibers can be expected to be lost in 4 hours with just 5% – 10% remaining at the end of 24 hours.

• Important to collect evidence from both complainants & suspects ASAP following alleged offense

Fiberspgs 59-65

• Fibers may be retrieved by tape lifts using clear adhesive tape pressed to the surface of the item or by vacuuming.

• Brushing & shaking aren’t recommended.

• Fibers can be collected on a sheet of clean, pre-folded paper that is then placed in an evidence bag or envelope & properly labeled.

Fiberspgs 59-65

• Value of fiber evidence demonstrated in Atlanta Child Murders case study.

• Proper collection & identification of distinctive series of fibers o the clothing of victims provided considerable information on the killer’s environment long before his arrest provided confirmation of the accuracy of the fiber evidence

Soil & Botanicalspg 66-72

• Other trace evidence that may be carried to or from a crime scene particularly on shoes or trousers includes soil evidence and what is broadly termed botanical evidence or simply “botanicals”.

• Soil – mixture of weathered and decaying rock, humus, other vegetable matter, and often particles of manufactured materials


• Humus – decomposed organic material

• Rock – minerals such as quartz, mica & feldspar

• Vegetable matter – bits of leaves, pine needles, plant stems, pollen grains, etc.

• Manufactured materials – asphalt, paint flakes, glass fragments, and so on


• Broad definition: “Soil may be thought of as including any disintegrated surface material, both natural and artificial, that lies on or near the earth’s surface.”

• Soil analysis depends on comparing questioned specimens with known samples.

Soil Profile

Soil Profile

• Most soils have three major horizons -- the surface horizon (A), the subsoil (B), and the substratum (C). Some soils have an organic horizon (O) on te surface, but this horizon can also be buried. The master horizon, E, is used for subsurface horizons that have a significant loss of minerals (eluviation). Hard bedrock, which is not soil, uses the letter R.

Soil Profile

Residue

Topsoil

OrganismsEarthwormsBacteriaFungi

Subsoil

Parent Material

Colored Coconut

Crushed ChocolateCookies

SprinklesGummy Worms

ChocolatePudding or Ice Cream

Candy coatedChocolate

SOIL PROFILE


• Criminalists consider gross visual appearance, comparing the color & texture of the sample, keeping in mind moisture darkens the color of soil, making it necessary that all samples be dried under exactly the same lab condition

• Low-power stereomicroscopic examination reveals various plant, animal & man-made materials contained in each sample.


• Technical microscopic examination requires knowledge of a geologist to use high-powered & polarized microscopy to identify rock & mineral particles.

• Size determination is accomplished by passing samples through a nested series of sieves, with opening size graduated from largest on top to smallest.


• Instrumental & chemical analysis use techniques such as spectrographic analysis, x-ray diffraction, differential thermal analysis, & both qualitative & quantitative chemical analysis.

• X-ray diffraction is used for analyzing crystalline materials such as minerals by measuring angle of x-ray diffraction


• Differential thermal analysis depends on a sample’s ability to absorb or release heat as it is continuously heated in a specially designed furnace over a wide temperature range.

• Some reactions take on heat (endothermic) while others give off heat (exothermic).


• Number of comparative points & frequency of occurrence must be taken into consideration before similarity between specimens can be concluded & the probability of common origin judged.

• Soils and related material are not generally individual type items such as fingerprints.


• Soil samples approach individuality when several methods are used & unusual minerals or combinations of minerals are found.

• Plant matter may be among the disintegrated materials making up soil, or it may be found as trace evidence on its own.


• Botanicals refers to anything of the vegetable class, for our purposes anything such as leaf fragments, pine needles, tree bark, weed stems, seeds or segments of seed pods, bits of moss or lichen, remnants of flower petals, & even pollen

• A close relationship exists between soils & vegetation. From the character of organic matter projections can be made as to the possible origin of organic material


• Pollen is especially useful in determining whether a suspect was in an area where particular flowering plants grow.

• Pollen grains may be collected by vacuuming the suspect’s clothes or by using clear adhesive tape in a grid pattern as with fibers.

• ID of pollen is accomplished by use of the laboratory microscope

Pollen Grain SEM


• Pollen comparison may be made with specimens collected from the scene, reference slides or from photomicrographs in published reference sources such as Walter C. McCrone’s monumental Particle Atlas.

• The investigator should consider whether a plant in question is pollinated by wind or insect

Soil & Botanicals


• Just because trace material doesn’t fall into an easily classifiable category doesn’t diminish evidential value.

• The tying of biological, mineral & vegetable matter to a suspect with the added weight of evidence resulted in an arrest & subsequent guilty plea.

Glass-Paint-Other Trace Evidence pg 72-75

• A variety of additional substances, virtually anything, may appear as trace evidence.

• Glass may play a role in a variety of crimes: a broken automobile headlight in a hit-and-run case, a smashed window in a burglary, or a fracture lamp in a homicide.


• Glass fragments-questions & known specimens-are compared for a common source of origin in a series of scientific tests that determine the chemical & physical properties of each.

• Microscopic determination may be made of the refractive indices.


• If both specimens refract (bend) rays of light at the same angle, they may be said to have the same refractive index.

• The respective densities may be determined by filling a tube with liquids of different densities arranged in order of heaviness with the densest on the bottom.


• The two particles to be compared are then introduced into the top of the tube, and if they float at the same level they may be considered to have equal densities.

• If the fragments are dissimilar in either refractive index or density, they can be excluded from having a common source


• The refractive index alone is highly distinctive as shown by almost 1,200 glass samples analyzed by the FBI laboratory

• It may be possible to demonstrate the commonality of larger fragments by fitting the pieces together like a jigsaw puzzle – called fracture matching.


• It is possible to determine from which side a bullet entered a pane of glass because there is a characteristic cone-shaped depression on the exit side

• As evidence, paint is commonly associated with breaking-and-entering and hit-and-run cases.


• Oil-based paints tend to produce smears• Automobile paint usually tend to chip.• A burglar may have paint (or varnish, etc.)

traces on his clothing as a result of the force used to pry open a door or open a cabinet or safe.

• If the tool used has a painted surface, traces of the paint may be left at the point of forced entry.


• If a painted object is used to assault someone, paint particles may be found on the victim’s clothing or in the wounds.

• Comparison of paint samples is usually effected in 1 of 3 ways: i.d. of chemical & physical properties; by number of coats; sequence of colors represented seen as layers in a chip; & fracture matching (fitting a chip or flake to an area of paint loss)


• Chemical/physical properties & number of coats are determined by comparing known questioned specimens side by side using a stereoscopic microscope.

• The color, texture of the surface, & sequence of color layers are the primary features of interest


• Pyrolysis gas chromatography can distinguish paint formulations.

• X-ray spectroscopy is an instrumental method useful for identifying the pigments in paint

• In collecting paint specimens the adhesive tape method should be avoided because it makes later separation difficult


• Scraping off of samples damages the layers and should not be undertaken.

• Instead, samples should be collected by chipping down to the surface of the underlying wood or metal.

• Paint samples should be removed with a wooden implement to avoid metal traces that would interfere with analysis.


• If necessary, a steel scalpel can be employed & delivered with the samples.

• In difficult cases, a small piece of the surface bearing the paint should be chipped or cut off.

Other Man-Made Materialspg 75

• There are various types of manufactured materials – cellophane, urethane foam, & blue olefin plastic

• This variety is too great to catalogue.• A short list would include rubber, concrete,

plaster, wire, other metal products, several platiscs including styrofoam, paper, soap, waxes & polishes, safe insulation, lipstick & other cosmetics, cigarette ash, etc.

The Atlanta Child MurdersCase Study pg 75-81

• Over a 22 month period beginning in July 1979, Atlanta, GA was the scene of the murders or disappearances of 30 African American children & young men.

• In time, investigators were on the track of a single killer. They began to notice on the clothing & bodies of the murder victims distinctive yellowish-green nylon fibers together with violet acetate fibers.


• It took until 1981 to determine the fibers came from a rug or carpet. (Keep in mind the newness of technology back then.)

• Wayne Williams was the suspect. His lie detector test produced inconclusive results

• The police found a book in his possession on how to beat a lie detector test


• A warrant was obtained to search the Williams’ home

• Fiber matches were made from a yellowish-green carpet fiber, fibers from Wayne’s bedspread and hairs from the family dog

• The carpet was made in Dalton, GA and sold in limited numbers in Atlanta area. Odds were limited


• In all, 28 different fibers, plus dog hairs, found on one or more victims were identified as consistent with 19 objects located in Williams’ home & automobile.

• The trial focused on two victims with evidence of 10 other victims permitted to be introduced linking them to the other two murders.


• At first it was thought to be the work of a white supremacist by the public.

• Witnesses testified they had seen Williams with some of the victims.

• Also, after his arrest, the killings stopped.

• Williams lost his temper on cross examination


• The jury deliberated for 11 hours before finding Wayne Williams guilty of both murders.

• He was sentenced to two life terms, which he is serving consecutively at the Valdosta Correctional Institution in southern GA

• Williams maintains his innocence. Fiber evidence suggests otherwise.


• Although the case has remained controversial, it set new precedents for the presentation of fiber evidence-indeed of trace evidence in general-that will no doubt help bring additional killers & other criminals to justice in the future.


• On 7-10-1988 the 6-year-old convictions of Williams were upheld. Prosecutors were accused of withholding evidence.

• Judge Hal Craig: “nothing has weakened the testimony about the scratches down petitioner’s arms consistent with defensive marks left by strangling victims.” He termed the fiber evidence “the strongest scientific link in this case.”

Fibers pgs 59-65 Fibers & cloth fragments offer much greater evidential value because they...

Documents

Transcript of Fibers pgs 59-65 Fibers & cloth fragments offer much greater evidential value because they...