Forensic in the Laboratory Midterm

What is the microscope?

Optical instrument that uses a lens or a combination of lenses to magnify and resolve the details of an object

What are the two lenses of a compound microscope?

Objective (lower) and eyepiece (upper) lenses

What is total magnification?

Objective lens magnification x eyepiece lens magnification

What is a stereomicroscope?

Offer enhanced depth perception and 3D viewing capabilities

What are the features of a stereomicroscope?

• 3D image

• Right-side-up image

• Magnification 10-125x

• Wide field of view

• Good depth of focus

• Large working distance

What is trace evidence?

Small transferable items that can be exchanged between people, places, or objects during a crime

Is latent evidence trace evidence?

No

What are the five uses of trace evidence?

1. Investigative aid

2. Association

3. Reconstruction

4. Transferred material

5. Pattern evidence

What does investigative aid refer to?

Origin/date of manufactured material, and geographic provenance

What does association refer to?

Link between individual scenes and/or items

What does reconstruction refer to?

Manner and/or place of contact

What does transferred material refer to?

Contact between surfaces, or by projection (contactless)

What are some examples of pattern evidence?

Burn marks, tire marks

What are the conditions that affect transfer evidence?

1. Pressure

2. Nature and number of contacts

3. Nature of material

4. Shed/form of evidence

5. Amount of material involved

What is Locard’s Exchange Principle?

Every contact leaves a trace

What is a direct transfer?

Evidence transferred from a source to a location with no intermediaries

What is an indirect transfer?

Evidence involving one or more intermediate objects

What is non-contact transfer?

Occurs when trace evidence becomes airborne and falls onto a surface

What is a pattern transfer?

When a pattern is the result of trace evidence (shoe prints, tool marks, indentation, striation, GSR)

What are the factors that affect the likelihood of transfer?

1. Nature of material

2. Shedding capabilities

3. Nature of receiving surface

4. Nature of contact

5. Number of contacts

6. Size of area of contact

Transfers will persist at a location until…

Further transfers or degradation occurs, or until it is collected as evidence

What are the factors of persistence?

1. Nature of accepting surface

2. Nature of transferred material

3. Environment/activity around evidence

4. Time from transfer of evidence

5. Force

How should trace evidence be collected if an entire item is intact?

Take everything containing potential evidence

How should trace evidence be collected when using gloves and tweezers?

Change gloves between evidence, and ensure no evidence is left behind on tweezers

How should trace evidence be collected when using vacuum sweeping and tape lifting?

Use clear tape, and package vacuum filter traps

What is electrostatic lifting used for?

Dust impressions

What are questioned/unknown evidence?

Evidence where original source is not known

What is known evidence?

Evidence where original source is known

What are controls and how are they used?

They are a known source that can be used for comparative purposes to unknown evidence, and may be positive or negative

What are some common trace evidence analysis methods?

1. Macroscopic examination

2. Compound/stereomicroscope

3. Close-up photos, measurements, and sketches

4. Determination of characteristics

How should trace analysis be conducted?

• Group items together based on who/where it came from

• Known and unknown should be analyzed separately

• Clean environment, use proper PPE

What does SWGMAT stand for?

Scientific working group on materials analysis

What is the purpose of SWGMAT?

Procedures for documentation, detection, collection, and preservation of trace evidence

What is identification?

Examination of the chemical and physical properties of a substance with as near absolute certainty as existing analytical techniques will permit

What is comparison?

Conducted to try and establish the source of the evidence – suspect and control do they have the same origin

• Gross physical properties

• Complex physiochemical mixtures

• Compositional analysis

What is classification?

Placing the evidence into a group of objects with similar characteristics and is associated with a common source

What is individualization?

An object classified into a group with only one member, and associated with a common source with an extremely high degree of probability

What is an investigative databank?

Collection of reference samples

What are interpretive databases?

Assigns significance of class evidence

How is fiber evidence found as?

• Shed or transfer of single fibers

• Threads lost, cut, or torn

• Textile product

What is analyzed when it comes to fiber evidence in forensics?

• Type of fiber based on physical, optical, and chemical properties

• Comparing unknown to known samples (controls)

• Examining construction of textile

  • Observing damage or mechanical fits

What is the basic unit of textiles?

Fibers

How are fibers defined as in relation to textiles?

Unit of material whose length significantly exceeds its width

What is involved in fiber production?

1. Processing materials into fibers

2. Spinning into threads/yarns

3. Construct twisted yarns, cordage or fabrics by a variety of methods

How are natural fibers processed?

Cleaned and then carded to separate fibres from each other and orient the fibres into the same direction to achieve a degree of order

What is carding?

Aligns the fibres, untangles clumps, and prepares the fibres to be spun

What is combing?

Refers to further alignment of fibres to prepare for spinning into yarns

What is cordage?

Refers to a general category of multiple threads or yarns twisted together into twine or rope

What is fabric?

Produced by weaving, knitting, or otherwise adhering fibres or yarns together into a textile material

What are the two most common types of fabrics?

Woven and non-woven

What are woven fabrics?

Involves a loom to create a textile material

What are non-woven fabrics?

Fibres are melted together to create a textile product

What are the two classification of fibers?

Natural and manufactured

What are natural fibers?

Any fibre that exists as a fibre in its natural state

• Vegetable

• Animal

• Mineral

What are manufactured fibers?

Any fibre derived by the process of manufacturing a substance that is not a fibre

• Synthetic

• Natural (bio)polymer

• Inorganic

What is the most common natural fiber?

Vegetable

What are the four main characteristics of fibers?

1. Crimp (waviness)

2. Color

3. Cross-sectional shape

4. Length

What is the most common natural fiber found at crime scenes?

Animal fibers

What is the most prevalent fiber?

Cotton

What are features of wool?

• Hair follicle of sheep

• Keratin

• Elastic

• Reduced medulla

• Higher water retention

• Great heat retention

What is keratinization?

Formation of DiS bonds

What are the features of silk?

• From lepidoptera

• Formed in larvae

• Held together by sericin

• Translucent with triangular cross-section

• Some variation

• Long

What are the features of cotton?

• Seed fiber from seed capsules ('“bolls”)

• Cell thickens due to deposition of cellulose

• Elongated single spindle-shaped cells

• Cell walls are variable thickness with variable twists along its length

• Convolutions

What are the features of flax, hemp, and kenaf?

• Stem made of bast fibers

• Fibers formed in bundles

• Held together by pectin

• Heterogeneous

• Differentiated by their cross-sectional shape and the twists in the fibres as it dries

What are features of asbestos?

• Fire resistant

• Mineral fiber found in mines

• Long

• Inhalation can lead to lung disease and cancer

How did manufactured fibers come about?

Introduced in 1911; Created from naturally-occurring polymers like cotton or wood pulp (regenerated fibres) or synthesized from simple starting materials/synthetic chemicals

What is a polymer?

Basic chemical substance of all synthetic fibres that can be made to assume different physical and chemical properties

What is acetate (polymer)?

A natural polymer that had been modified from cellulose (acetylated), and is often blended with cotton and other synthetics

What is viscose/rayon?

A very soft, cellulose-derived fiber that consists of a silk-like appearance and handling

What is polyester?

Synthesized from diol with ester-linkage along the polymer chain backbone with a high melting point, fine and translucent fibers, hydrophobic, and is very strong

What is polypropylene/olefin?

A type of polyolefin polymerized from petroleum-based products that is highly resistant to chemical degradation, has a large diameter, and smooth surface

What is nylon?

A thermoplastic material that can melt under high heat/friction, and is lustrous, waterproof, and resistant to sunlight and weathering

What are semi-synthetic (biopolymer) fibers?

Regenerated forms of cellulose or partial oxidation of cellulose

What are the factors of persistence and transfer of fiber evidence?

1. Surface type and area of contact

2. Number of contacts

3. Force/intensity of contact

4. Nature of donor material

5. Time elapsed/movements since transfer

6. Contact of recipient surface after transfer

What are the three mechanisms of fiber transfer?

1. Transfer of already loose fibers

2. Pulling of fibers via friction

3. Fragmentation upon contact

How long do most transferred fibers last in normal environmental conditions?

Approximately two hours

What are the four main types of textiles?

1. Protein

2. Cellulosic

3. Mineral (inorganic)

4. Synthetic

What are protein textiles made of?

Amino acid polymers

What are cellulosic textiles made of?

Carbohydrate polymers

What are mineral/inorganic textiles made of?

Materials obtained from rocks or sands

What are synthetic textiles made of?

Made of polymers that originate from small organic molecules that combine with water and air

What are the two classifications of fiber length?

Filament and staple fibers

What are filament fibers?

Indefinite or extreme length (usually natural fibers)

What are staple fibers?

Natural fibers that cut lengths of filaments

What is yarn?

Continuous strands of textile fibres, filaments, or material in a form suitable for entangling with another yarn to form a fabric

What are woven fabrics made of?

Two sets of yarn (warp and weft)

• Warp = Runs lengthwise

• Weft = Runs crosswise

What are knitted fabrics made of?

Constructed of interlocking series of loops of one or more yarns

What are the two types of knitted fabrics?

Courses = Rows of loops along width of fabric

Wales = Rows of loops along length of fabric

What are some common fiber collection methods?

1. Forceps, picking, visual examination

2. Tape lifts

3. Vacuum

4. Comb

5. Shaking/scraping

What does stereomicroscopes reveal about fibers?

General characteristics

What does a bright field/comparison microscope reveal about fibers?

Comparison of morphology, diameter, and color

What does a polarizing light microscope reveal about fibers?

Optical properties

What does a fluorescence microscope reveal about fibers?

Fluorescent properties

What does a scanning electron mis\croscope reveal about fibers?

Identify fibre form/surface structure by exposing it to an electron beam

What does a microspectrophotometer reveal about fibers?

Objective color analysis

What are the physical and chemical characteristics of fibers?

1. Diameter

2. Cross section

3. Color/application

4. Treatment

5. Weathering

6. Length

What are three main tests used for fiber analysis?

Melting points, solubility, and burn tests

What is the value of textile damage?

Fabric damage characteristics will reflect their original cause

What are the three categories of textile/fabric damage?

1. Mechanical

2. Chemical

3. Heat

What are the most common types of textile damage?

Tear, puncture, abrasions