Name:Date:

REVIEW: FIBER, HAIR AND FINGERPRINTS

FIBER

  1. A gray cotton fiber was found on the red sweater of a victim. A gray cotton fiber was taken from a suspect’s sweatshirt. After testing 280 gray sweatshirts, the lab found the fiber matched 28 of them. What is the probability that the crime scene fiber and that of the suspect matched simply by chance?

1/10, not very favorable for a conviction, but perhaps there is more circumstantial evidence

  1. Can a fiber be individualized to a particular textile fabric? Why or how?

No, textile fabrics are mass produced. If something unique was associated with the textile, such as a particular fluorescence, then individualization may be possible

  1. Can a piece of fabric be individualized to a particular garment? Why or how?

Yes, a sample can be individualized when a piece of fabric torn from a garment can be matched directly to the tear pattern, like a piece in a jigsaw puzzle. This is a physical match. Another way you can individualized particular fabric sample would be if there were blood, paint or something peculiar absorbed to the garment.

  1. Many fibers look very similar under the microscope, but there are major differences between synthetic and natural fibers. What would you look for in determining whether a particular fiber was synthetic or natural?

Consistency, whether the fiber in consistent in diameter, shading as

Well

  1. Out of seven analytical tests performed to match a questioned fiber to a known, you find one discrepancy; for example, the cross-section is triangular rather than round. What do you do?

Repeat the test to verify the difference. Analyze the questioned and known samples at the same time to minimize experimental and observational uncertainties. If there is still a discrepancy, then there is no match, and no association between suspect, victim, location based on fiber evidence.

  1. All else being equal, which fiber has the more probative value, polyester or an acrylic fiber? Why?

Polyester makes up 58% of ~8 billions pounds of human made fiber produced in US. Acrylics account for 8%. Therefore the probability of finding a random acrylic fiber is 7 to 1 less than finding an unassociated polyester fiber. Investigators can never say with any certainly that a fiber originated from a particular textile to the exclusion of all others; however, any factor that decreases the probability of an accidental association increases the significance of findings.

  1. Why are fibers considered class evidence?

Because it is difficult to individualize them to a particular fabric due to the mass market production of fibers.

  1. How can fibers be used as circumstantial evidence to link the victim, suspect, and crime scene?

Can provide corroborating evidence, statistical analysis can play a large part

  1. What are the two main classes of fibers? Give several examples of each.

Natural (wool, silk, cotton, angora, cashmere, alpaca)

man made (nylon, polyester, acrylic)

  1. How can the classes of fibers be identified?

Fibers can be identified as man made or natural. Natural fibers are not consistent throughout, nature is not perfect. Man made fibers are consistent throughout their length since during their manufacture they are protruded through a nozzle, determining the shape of the fiber.

  1. Why are statistics important in determining the value of evidence?

Statistics provides a means to evaluate how relevant a certain piece of evidence is. Does it help prove a defendant is guilty? Often, there is a lot of evidence, even circumstantial, however, statistically speaking each piece individually may not mean much, but together can pinpoint a criminal.

  1. You observed several different types of fibers, which samples were natural fibers? Which samples were synthetic fibers?

Natural : Wool, silk, cotton, burlap, linen

Manmade: rayon, polyester, nylon, acrylic

  1. What fibers can also be considered hair?

Wool, angora and mohair

  1. How do class and individual evidence compare?

Individual evidence can be class evidence as well, but it has characteristics that make it unique to a particular situation

  1. Describe why the Wayne Williams case was ground breaking in terms of forensics?

The use of fiber evidence as the main basis for the case against him rather than as supportive

HAIR

  1. What is the morphology of hair?
  1. Draw and identify the cuticle, cortex and medulla of hair.
  1. Illustrate the different types of medullae.

continuous; interrupted; fragmented

  1. If you were asked whether a particular hair sample was human or animal, what would you look for? Explain using words and diagrams.
  1. Compare and contrast the ends of a fallen out hair, a pulled out hair and a cut hair.
  1. Choose three characteristics of human hair and describe how each one can be used to identify one hair from another.
  1. What characteristics make hair a useful forensic tool?
  1. If you were asked to compare an unknown(questioned) sample to a know sample of human hair to match or identify origin, what would you look for? Would your observations give conclusive evidence? Explain using words and drawings.
  1. Can the area a body hair is from be indentified? Why or why not?
  1. Can hair be used to determine race? Why or why not?
  1. Can hair be used to determine age or sex? Why or why not?
  1. Be able to define: cortex, medulla, hair follicle, shaft, cuticle

FINGERPRINTS

  1. State the three Fundamental Principles of Fingerprints.
  1. Explain how and why fingerprints are found on objects which have been touched.
  1. Explain the procedure, theory, and appropriate surface of use for each type of latent print development:

Dusting, Ninhydrin Spray, Iodine Fuming, and

Reacting with silver nitrate and UV light.

  1. What are the three types of prints and how is each made?
  1. What are the three different patterns of fingerprints? Briefly describe each.
  1. How are fingerprints classified?
  1. Identify the seven minutiae in the print below:

  1. Be able to define the following:

Accidental, whorl, delta, core, arches, radial loop, ulnar loop, AFIS, loop, latent prints, plastic prints, visible prints, minutae, dusting, fuming