Lecture 7: Physical Evidence I (Fibres) Flashcards
What is Forensic Science?
The application of scientific principles and techniques to investigate and analyze physical evidence from crime scenes.
What are common types of physical evidence?
- Blood, semen, & saliva
- Documents
- Drugs
- Explosives
- Fibers
- Fingerprints
- Firearms & ammunition
- Glass
- Hair
- Impressions
- Organs & physiological fluids
- Paint
- Petroleum products
- Plastic bags
- Plastic, rubber, polymers
- Powder residues
- Serial numbers
- Soil & minerals
- Tool marks
- Vehicle lights
- Wood & other vegetative matter
What are fibers considered in forensic science?
- Solid objects
- Thin, flexible, elongate
- Resistant to degradation
- Trace evidence
What are the two main classifications of fibers?
Natural and man-made fibres
What is an example of a natural fiber?
Wool (from sheep), mohair (from goat), and cotton.
What are regenerated fibers?
- Examples: rayon, acetate, triacetate
- Manufactured from natural sources by altering natural fibers.
What are synthetic fibers?
- Examples: nylons, polyester, acrylics
- Produced solely from synthetic chemicals, e.g. polymers
How can fibers be collected from a crime scene?
- Special vacuums
- Sticky tape
- Lint rollers
- Forceps
- Hand picking with tweezers
What information can fiber analysis provide?
- Type of fiber
- Color
- Possibility of violence
- Location of suspects
- Point of origin
True or False: The value of fiber evidence depends on the analyst’s ability to narrow down its origin.
True
What are the two main methods of analyzing fibers?
- Non-destructive: Microscopes, infrared spectroscopy
- Destructive: Melting point, dye extraction
What is a compound microscope used for?
To magnify and resolve fine details of objects.
What is the role of a comparison microscope?
To observe two specimens side-by-side for comparison.
What does a polarizing microscope do?
- Determines how polarized light interacts with a sample
- Examine characteristics (e.g. shape, color, size)
- Identify hair, human-made fibers, paint
What is a scanning electron microscope (SEM)?
A microscope that uses a beam of electrons to produce high-magnification images.
What is the significance of cross-sectional shape in fibers?
No two of the same type of fibers are manufactured the same way
In the Atlanta child murders case, what type of evidence helped solve the case?
Cross-sectional shape of fibers: No two of the same type of fibers are manufactured the same way
Fill in the blank: Fibers are classified as ______ evidence.
trace
What is the primary advantage of using non-destructive testing methods?
They preserve the original evidence for further analysis.
What is the importance of the color and diameter of fibers in forensic analysis?
They can be compared to standard/reference samples to establish links, under a comparison microscope
Name some morphological features of fibres
- Different scales of natural fibers derived from different animals
- Little variation in synthetic fiber due to precise machinery
- Delustering particles (TiO2) to reduce shine
