FORENSIC SCIENCE Trace Evidence

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FORENSIC SCIENCETrace Evidence
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Introduction

• Trace Evidence--any small pieces of material,
  man-made or naturally occurring
• Most common examples
• Hair
• Fiber
• Guiding principle
• Every contact leaves evidence behind

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Test Questions for Trace Evidence

• What is it?
• Is it man-made or natural?
• What is its source?
• How common is it?
• Can it be identified to a single source?

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Hair

• Human hair
• one of the most frequently found pieces of
  evidence
• provide a link between the criminal and the act.
• From hair, one can determine
• Human or animal
• Race
• Origin
• Manner in which hair was removed
• Treated hair
• Drugs ingested

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DNA

• The hair shaft contains abundant mitochondrial
  DNA. It can be typed by comparing relatives if no
  DNA from the body is available.
• Only the root contains nuclear DNA.

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Hair Morphology The Study of Structure and Form

• Parts of the hair
• Shaft--part of the hair that sticks out of the
  skin
• Root--lies below the skin
• Follicle--structure from which the hair grows

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Hair Cuticle

• Types of cuticles
• Mosaic
• Pectinate
• Imbricate
• Petal
• Diamond petal
• Chevron

The cuticle is the outermost layer of hair which
is covered with scales. Scales also always
point toward the tip of the hair. These scales
differ between species of animals.
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Scale Types
Mosaic
Chevron
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Scale Types (cont)
Pectinate
Imbricate
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Scale Types (cont)
Petal
Diamond Petal
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HUMAN SCALES

• In order to visualize the scales
• paint fingernail polish on a slide
• place a hair on the polish
• lift off the hair and observe the scale imprints
• What pattern is seen in this slide?

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Hair Cortex

• The cortex gives the hair its shape.
• It has two major characteristics
• Melanin--pigment granules that give hair its
  color
• Cortical fusi--air spaces, usually found near the
  root but may be found throughout the hair shaft

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Hair Medulla

• The medulla is the hair core that is not always
  present. The medulla comes in different types
  and patterns.
• Types
• Continuous
• Intermittent or interrupted
• Fragmented
• Absent--not present

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HUMAN MEDULLA

• Human medulla may be continuous, fragmented or
  absent.

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Medullary Index

• Determined by measuring the diameter of the
  medulla and dividing it by the diameter of the
  hair.

Medullary Index for human hair is generally less
than 1/3. For animal hair, it is usually greater
than 1/2.
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Hair Comparison

• Color
• Length
• Diameter
• Distribution, shape and color intensity of
  pigments
• Dyed hair has color in cuticle and cortex
• Bleaching removes pigment and gives yellow tint

• Scale types
• Presence or absence of medulla
• Medullary type
• Medullary pattern
• Medullary index

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Hair Toxicology (Drug testing)

• Advantages
• Easier to collect and store
• Is externally available
• Can provide information on the individuals
  history of drug use.
• Collections must be taken from different
  locations on the body to get an accurate timeline.

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HAIR TESTINGProcedure

• Collect an adequate sample, cut as closely to the
  scalp as possible.
• Wash the hair to remove lipids, oils, cosmetics
  and any drugs adhering to it
• Cut it into one centimeter sections
• Place hair in a digesting solution
• Screening test--antibodies are added to the hair
  that bind with the drugs. If this shows that
  drugs are present
• A confirmation test is done by gas chromatograph
  and then a mass spectrometer.

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Fiber Evidence

• NOTE Fabric is the type of material and fibers
  are the threads that make up the fabric
• The use of fiber evidence in court cases is used
  many times to connect the suspect to the victim
  or to the crime scene. In the case of Wayne
  Williams, fibers were the entire case. Williams
  was convicted in 1982 based on carpet fibers that
  were found in his home, car and on several murder
  victims. Although this case is unusual, fibers
  are generally considered of greater value as
  evidence than that of rootless hairs since they
  may contain a greater number of variables, thus
  showing more individual characteristics.

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Types of Fibers

• Natural
• Silk
• Cotton
• Wool
• Mohair
• Cashmere

• Synthetic
• Polyester
• Rayon
• Nylon
• Acetate
• Acrylic
• Spandex

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Classification

• Classified according to their origin
• Vegetable or cellulose
• Animal or protein
• Mineral

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Cellulose Fibers

• Cotton--vegetable fiber. Strong, tough,
  flexible moisture absorbent not shape retentive
• Ramie--vegetable fiber. Less flexible than cotton
  so its often blended with cotton
• Rayon--first man-made fiber soft, lustrous,
  versatile fiber
• Acetate--less expensive, less polluting than
  rayon

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Fiber Comparison
Can you tell the difference(s) between the cotton
on the left and the rayon on the right?
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Petroleum Plastics(Made from derivatives of
petroleum, coal and natural gas)

• Nylon--most durable man-made fabric extremely
  light weight
• Polyester--most widely used man-made fiber
• Acrylic--provides warmth from a lightweight, soft
  and resilient fabric
• Spandex--extreme elastic properties
• Fleece made from recycled plastics

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Protein Fibers

• Wool--animal fiber coming most often from sheep
  but may be goat (mohair), rabbit (angora), camel,
  mink
• Silk--animal fiber that is spun by a silk worm to
  make its cocoon fiber reflects light and has
  insulting properties

Wool Fibers (400X)
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Mineral Fibers

• Asbestos--a natural fiber that was used in
  fire-resistant substances
• Metallics (mylar)--a manufactured mineral fiber
• Fiberglass--another manufactured mineral fiber

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Fabric Characteristics

• All unique to type of fabric
• Loop pattern
• Knitted
• Woven
• Bonded
• Crocheted
• Felted
• Knotted
• laminated

• Types of fibers
• Degree of stretch
• Absorbency
• water repellence
• Softness
• durability

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Identification andComparison of Fibers

• Microscopic examination
• Color--compositional differences in the dyes
• Fibers surface--delustering particles that may be
  added by manufacturers
• Microspectrophotometer--compares fiber colors
  through spectral patterns
• Chromatography--gives a more detailed analysis of
  the dye composition

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Man, I was nailed when those forensic guys found
fibers from the kids math assignment in my
teeth.