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Intro to Forensic Science > Material Evidence > Flashcards

Material Evidence Flashcards

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1
Q

Material Evidence is also referred to as:

A

trace evidence

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2
Q

Material Evidence

A

transfer of a small quantity of material possible; may not always be detected

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3
Q

Material Evidence Items include but are not limited to:

A 
Paint
Hair 
Fiber
Glass
Soil 
Fabric
Gunshot Residue
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4
Q

How can the transfer occur?

A

1) Locard’s Principle of Exchange

2) Contact does not have to be involved in order for materials/trace evidence to be left behind (deposit)

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5
Q

Deposit Examples

A

GSR
Pollen
Dust
Hair/Fiber

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6
Q

What is a hair?

A

a long, slender outgrowth from the follicles of mammals

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7
Q

What is hair composed of?

A

Keratin

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8
Q

What does hair cover on a human?

A

All parts except for palms of hands, soles of feet, and lips

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9
Q

What does hair protect?

A

eyes, nose, head

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10
Q

Observation of physical / structural characteristics =

A

morphology

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11
Q

Morphology

A 
color
size
tip
root
damage
artifacts
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12
Q

Can hair be individualized based on its morphology?

A

NO

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13
Q

A “match” should be confirmed by:

A

DNA analysis (if possible)

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14
Q

1996-2000

A

Study of hair evidence submitted to FBI by microscopy and DNA

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15
Q

____ or _____ of microscopic matches were non matches when DNA was performed

A

~11% or 9/80

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16
Q

The shaft of the hair is composed of three layers:

A

Cuticle
Cortex
Medulla

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17
Q

Cuticle

A
  • Outside covering of hair
  • Keratinized (hardened) cells
  • resistance to chemical decomposition
  • able to retain physical structure over time
  • can examine with SEM or with a cast/compound microscope
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18
Q

Cuticle of human hair v animal hair

A

Not an individualizing characteristic

More important in the recognition and identification of animal hair/species identification

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19
Q

Cuticle of human hair v animal hair

A

Not an individualizing characteristic

More important in the recognition and identification of animal hair/species identification

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20
Q

Cortex

A
  • Contained inside the cuticle
  • made up of spindle shaped corticle cells
  • aligned in a regular fashion
  • aligned parallel to the shape of the hair
  • Embedded with pigment granules (hair color)
  • Color, shape, and distribution of granules are used as points of comparison among different individuals
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21
Q

Medulla

A
  • runs through center of hair
  • can be present in animal and human hair
  • cylindrical
  • varying shapes
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22
Q

Medullary index

A

Human medullas 1/2 or greater

23
Q

Human Hair - 3 types

A
  1. Caucasoid
  2. Negroid
  3. Mongoloid

Categories based on the origin

24
Q

Roots

A

provide the necessary tools for hair production and growth

25
Q

Shape and size are dependent on the phase of growth that the hair is in:

A
  1. anagen
  2. catagen
  3. telogen
26
Q

Anagen Phase

A
  • root attached to the follicle
  • continued growth
  • may last up to six years
  • root bulb has a flame shaped appearance
  • may have a follicular tag when pulled from the root
27
Q

Catagen Phase

A
  • continued growth, but slowed
  • may last from 2-3 weeks
  • transition stage between anagen and telogen
  • roots appear elongated as the root bulb shrinks
28
Q

Telogen phase

A
  • begins once hair growth ends
  • hair is pushed out of the follicle
  • hair will naturally shed
  • may take two to six months
  • root takes on a club shaped appearance
29
Q

What forensic significance does root examination have?

A

Forcibly pulled vs. shed (struggle)

30
Q

Presence of follicular tag =

A

DNA

31
Q

Fibers

A

may be the most common kinds of materials evidence found

  • used in commerce
  • easily broken
  • sticks to other objects easily
  • commonly transferred through contact
  • light
  • will catch onto rough objects
32
Q

Two classifications of fibers

A

Natural and Synthetic

33
Q

Examples of natural fibers

A

Animal
Vegetable
Mineral

34
Q

Animal fibers

A

All animal fibers are protein

35
Q

Vegetable fibers

A

All vegetables fibers are cellulose

36
Q

Mineral fibers

A
  • Not as common as the other two, generally not of forensic interest
  • abestos and mineral wool (insulation purposes)
37
Q

Synthetic fibers

A
  • Began with the introduction of Rayon in 1911
  • 1939: Nylon developed
  • can be regenerated fibers (produced from regenerated Cellulose)
  • Polymers
38
Q

Regenerated fibers

A

made from natural fibers and chemically processed (Rayon, Acetate, Triacetate)

39
Q

Polymers

A

basic chemical substance of all synthetic fibers (Nylon, Polyester, Acrylic)

40
Q

What is involved in the microscopic examination of fibers?

A 
Morphology 
Color
Texture 
Sheen 
Dye Composition 
Refractive index 
Infrared Spectroscopy
41
Q

Chemical composition tests

A

Do questioned fibers belong to the same generic class of fibers?

Do questioned fibers belong to the same subclassifications within that generic class?

42
Q

Example: Nylon

A

There are four different times of Nylon

Each differ in physical shape, appearance, and dyeability because of differences in their chemical structures

43
Q

Infrared Absorption

A

Use of an IR microspectrophotometer

Can determine the absorption

Non destructive

44
Q

What are the most common sources of hair and fiber evidence?

A

Clothing and vehicles

45
Q

Clothing can be the source of materials evidence for:

A
  • homicide
  • sexual assault
  • assault
  • mugging
  • motor vehicle/hit and run
  • motor vehicle accidents (driver)
  • any incident where there is potential contact with clothing can be important
46
Q

First step in collection/processing

A

RECOGNITION

47
Q

Collection methods in material evidence

A

Forceps/tweezers
Tape lifting
Mechanical dislocation
Vacuuming

48
Q

Forceps/Tweezers

A
  • Manually picking off the evidence with a pair of tweezers
  • Always record where the evidence came from on the item
  • May be aided with the use of an ALS and/or magnification
  • Allows for collection without extraneous materials from the object
49
Q

Tape Lifting

A
  • Utilizes adhesive tape
  • Tape should be sticky, but not too sticky
  • Will remove foreign material from the surface, and not a lot of background
  • Stereomicroscope used to examine tape lift
  • Evidence can be individually cut out, collected by tweezers
  • Removal is aided by using solvent to dissolve adhesive
  • Commercially available through venders
  • Or lint roller
50
Q

Mechanical dislocation

A
  • involves vigorous shaking or scraping of item of evidence to remove foreign materials
  • clean piece of paper
  • material on paper examined using stereomicroscope
  • material can be sorted easily - type, color, etc
51
Q

Hair should be pulled from:

A

the root (not cut)

  • Length of hair from root to tip may be important
  • Forensic examination of root structure (microscopic)
52
Q

In what increments should hair be collected?

A

Four areas of the head

5-10 pulled per area

53
Q

Examination of hair evidence

A
  1. Microscopy (exclusionary, consistent with/associated with)
  2. DNA (use calls on root of hair, mtDNA)

Intro to Forensic Science (12 decks)

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