trace and contact evidence part 1: recoverable materials

Question 1

give the 5 ways that fibres can be recovered

Answer 1

1. hand picking w/tweezers
2. vacuum
3. scraping
   4.combing
4. tape lifts

Question 2

where should control hair samples be taken from an individual

Answer 2

from all body locations

Question 3

what is the purpose of microscopic examination of fibres?

Answer 3

1. identify fibre type e.g human hair, nylon
2. provide description of characteristics for comparison with control

Question 4

what are the 3 main morphological features of hair + describe the whereabouts they are on a strand of hair

Answer 4

1. cuticle (outer)
2. the cortex (middle)
3. the medulla (inner)

Question 5

give 3 forensic opportunities of hair

Answer 5

1. colour of shaft can determine whether human or non-human, human= little variation
2. width of medulla can determine if human, medullary index less than a 1/3 for humans
3. morphology can deduce which part of the body the hair originated from
4. distinction of whether hair was forcefully removed- anagen, telogen

Question 6

what are 3 ways you can analyse fibres?

Answer 6

1. comparison microscope
2. dye extraction followed by TLC
3. scanning electron microscopy- details of surface morphology
4. Ashing of natural fibres

Question 7

how would you know which way the direction of a projectile came from in broken glass?

Answer 7

damage is characterized by a crater-shaped hole of the impact that is narrowest on the side of impact

Question 8

what is the issue with determining the side of impact using the narrowest crater shaped hole as the side of impact?

Answer 8

as the velocity of the projectile decreases the shape of the hole becomes less regular so tf can not establish side of impact

Question 9

how can you tell where the impact occurred on glass using stress marks?

Answer 9

radial cracks and concentric cracks form on the side opposite to where the impact occurred

Question 10

what are the collection methods of glass?

Answer 10

1. combing suspects hair/clothing
2. hand searching + shaking garment over a clean sheet of paper of funnel

Question 11

what are two analysis methods of glass that can reveal class characteristics of glass?

Answer 11

1. density
2. refractive index

Question 12

describe how density of glass can establish class characteristics

Answer 12

1. questioned glass is placed in medium of liquids w different densities
2. density of medium is adjusted by addition of one or the other liquids until fragment is suspended in the medium
3. when suspended, density of medium is identical to fragment
4. questioned glass is removed
5. control glass is added
6. if it sinks of floats, it is not the same as questioned glass