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FORB201 > Lecture 7 - Trace and Contact Evidence > Flashcards

Lecture 7 - Trace and Contact Evidence Flashcards

1
Q

What are the 3 categories of forensic evidence?

A
  • Biological
  • Physical
  • Impression
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2
Q

What are some visual screening techniques for searching evidence?

A
  • Sunlight
  • White light/torch
  • Oblique light
  • Crime lite
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3
Q

What is a crime lite?

A

Hand-held, high intensity light source

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4
Q

How does a crime light work?

A

Filters wavelengths allowing forensic evidence to be targeted

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5
Q

What are 3 examples of things crime lites can detect?

A
  • Blood
  • Semen
  • Saliva
  • Bone
  • Teeth
  • Hair
  • FIbres
  • Shoe print
  • FIngerprints
  • Gunshot residue
  • Accelerants
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6
Q

What is biological evidence?

A

Body fluids or cells containing DNA which can be used for identification purposes

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7
Q

What are 3 bodily fluids that can be chemically tested?

A
  • Blood
  • Saliva
  • Semen
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8
Q

What chemical tests are used for blood?

A
  • Combur
  • Kastle Meyer
  • Luminol (often used last)
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9
Q

How does the Combur test work?

A
  • Catalytic reaction of haemoglobin on a peroxide substrate
  • Colour change from yellow to green
  • Sensitive but not specific
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10
Q

How does the Kastle Meyer test work?

A
  • Phenolphthalein is used to detect possible presence of haemoglobin
  • Colour change to pink
  • Less sensitive but more specific
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11
Q

How does Luminol test work?

A
  • Reacts with iron in haemoglobin causing luminescence
  • Non-specific, other substances may react including bleach, copper and horseradish
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12
Q

What chemical test is used for saliva?

A

Phadebas

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13
Q

How does the Phadebas test work?

A
  • Saliva is rich in the enzyme alpha-amylase (a-amylase)
  • Phadebas test reacts to a-amylase by releasing blue dye
  • Presumption test indicating saliva may be present (amylase is found in other body fluids at lower levels)
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14
Q

What chemical test is used for Semen?

A

Acid phosphatase (ACP)

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15
Q

How does the Acid Phosphatase test work?

A
  • ACP is found in high concentrations in semen
  • Suspect stain is sampled by swab or damp blotting paper and a solution (sodium alphanapthylphosphate and fats blue B) is applied
  • Purple blue colouration if positive
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16
Q

What to do when collecting biological evidence?

A
  • Risk assessment (safety always before evidence)
  • PPE (gloves and mask minimum)
  • Records (photos and notes)
  • Use sterilised/sterile equipment
17
Q

How would you collect blood sample?

A

One wet swab using sterile water

18
Q

How would you collect saliva sample?

A

Two swabs - one wet then one dry

19
Q

How would you collect trace/touch sample?

A

Two swabs - one wet then one dry

20
Q

How would you collect cigarette butt?

A

Entire item into envelope/plastic pottle

21
Q

How would you collect clothing?

A

Entire item into paper bag

22
Q

What is physical evidence?

A
  • Physical, microscopic and chemical evidence
  • Tangible items which can be collected from a crime scene
23
Q

What are some examples of physical evidence?

A
  • Glass
  • Paint
  • FIbres
  • Soil and pollen
  • Hydrocarbons
  • Gunshot residue
  • Explosives
24
Q

What is physical fit?

A
  • Pieces left at a scene that can be linked back to the source
  • Physically fitting the pieces back together
  • Like a jigsaw puzzle
25
Q

In what 5 situations could glass be left behind?

A
  • Hit and run
  • Ram raid
  • Assault with bottle
  • Broken windows
  • Smashed windows
26
Q

How is glass linked back to its source?

A
  • Refractive index
  • Density
  • Thickness
  • Colour
  • Physical fit
27
Q

What percentage of glass backscatter is there likely to be?

A

30%

28
Q

What should glass be packaged in?

A

Plastic bottle/container

29
Q

What is the glass compared to? (control samples)

A
  • Control (or reference) sample from broken window
  • Refractive index varies slightly across a window
  • 10 samples taken from around the window
  • Not from the ground
30
Q

In what situations could paint often be left behind?

A
  • Hit and run
  • Ram raid
  • Assault with painted object
  • Burglary
31
Q

How is paint linked back to its source?

A
  • Layers
  • Colours
  • Microscopy
  • Physical fit
32
Q

What is the paint compared to? (control samples)

A
  • From damaged panel
  • Away from the area of damage
  • Multiple samples
  • All layers, down to the base
33
Q

What is impression evidence?

A

Contact between two surfaces leaving a mark which can be used for identification purposes

34
Q

When can tool marks occur?

A
  • When used to force open a window or door
  • Softer surfaces
  • Burglary
35
Q

How are tool marks collected?

A

A cast is created by putting a paste in the tool mark, letting it dry and peeling it off

36
Q

What are the class characteristics when linking tool marks to tools?

A
  • No damage
  • Original condition
  • Type and size of tool used
37
Q

What are the individualizing characteristics when linking tool marks to tools?

A
  • Wear and damage
  • Microscopy used
  • Type, size and specific tool used
38
Q

What are the class characteristic when linking shoeprints to shoes?

A
  • No damage
  • Size and make of shoe
39
Q

What are the individualising characteristic when linking shoeprints to shoes?

A
  • Wear and damage
  • Size, make and specific shoe

FORB201 (18 decks)

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