Fiber and Threads

1
Fiber and Threads

• How are fibers found at a scene helpful?
• Why would fibers be less than helpful when found
  at a scene?

2
Types of Fibers

• Natural fibers derived from plants or animals
• Manufactured fibers fibers derived from either
  natural or synthetic polymers

3
Natural Fibers

• Which type of natural fibers do you think are
  most often encountered at crime scenes?
• Hair
• Fur
• Use microscopic analysis to identify
• What is the most prevalent PLANT fiber?

4
Cotton Fiber
5
Identification and Comparison of Manufactured
Fibers

• 1st Step Microscopic Examination of fibers
• To compare color and diameter
• Uses a comparison microscope
• If negative, no point going further.

6
Microscopic Examination

• Other features to compare
• Lined markings on the surface
• Pitting of the surface
• Cross-sectional (???) shape
• Comparison of dye composition of same-colored
  fibers
• Microspectrophotometer
• Chromatographic separation of the dye constituents

7
Identification and Comparison of Manufactured
Fibers

• 2nd Step Chemical Composition to determine and
  compare what class of fibers each sample belongs
  to.
• 3rd Step Other, more complicated tests

8
Significance of Fiber Evidence

• Does a fiber match mean the fiber came from the
  garment in question?
• What are the chances that a match - including
  size shape, microscopic appearance, chemical
  composition, and dye content - would be wrong?

9
Collection of Evidence

• How?
• Bag whole articles separately clothing,
  bedding, carpets, car seats, etc.
• Remove stray fibers
• Either way, VERY tedious and time-consuming

10
Forensics at Work

• Jeffrey MacDonald
• The Telltale Rabbit