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Intro to Forensic Science > Material Evidence > Flashcards

Material Evidence Flashcards

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
Shape and size are dependent on the phase of growth that the hair is in:
1. anagen 2. catagen 3. telogen
26
Anagen Phase
- 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
Catagen Phase
- 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
Telogen phase
- 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
What forensic significance does root examination have?
Forcibly pulled vs. shed (struggle)
30
Presence of follicular tag =
DNA
31
Fibers
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
Two classifications of fibers
Natural and Synthetic
33
Examples of natural fibers
Animal Vegetable Mineral
34
Animal fibers
All animal fibers are protein
35
Vegetable fibers
All vegetables fibers are cellulose
36
Mineral fibers
- Not as common as the other two, generally not of forensic interest - abestos and mineral wool (insulation purposes)
37
Synthetic fibers
- Began with the introduction of Rayon in 1911 - 1939: Nylon developed - can be regenerated fibers (produced from regenerated Cellulose) - Polymers
38
Regenerated fibers
made from natural fibers and chemically processed (Rayon, Acetate, Triacetate)
39
Polymers
basic chemical substance of all synthetic fibers (Nylon, Polyester, Acrylic)
40
What is involved in the microscopic examination of fibers?
``` Morphology Color Texture Sheen Dye Composition Refractive index Infrared Spectroscopy ```
41
Chemical composition tests
Do questioned fibers belong to the same generic class of fibers? Do questioned fibers belong to the same subclassifications within that generic class?
42
Example: Nylon
There are four different times of Nylon Each differ in physical shape, appearance, and dyeability because of differences in their chemical structures
43
Infrared Absorption
Use of an IR microspectrophotometer Can determine the absorption Non destructive
44
What are the most common sources of hair and fiber evidence?
Clothing and vehicles
45
Clothing can be the source of materials evidence for:
- 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
First step in collection/processing
RECOGNITION
47
Collection methods in material evidence
Forceps/tweezers Tape lifting Mechanical dislocation Vacuuming
48
Forceps/Tweezers
- 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
Tape Lifting
- 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
Mechanical dislocation
- 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
Hair should be pulled from:
the root (not cut) - Length of hair from root to tip may be important - Forensic examination of root structure (microscopic)
52
In what increments should hair be collected?
Four areas of the head | 5-10 pulled per area
53
Examination of hair evidence
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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