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FORB201 > Lecture 7 - Trace and Contact Evidence > Flashcards

Lecture 7 - Trace and Contact Evidence Flashcards

1
Q

What is Locard’s Exchange Principle?

A

With contact between two items there will be an
exchange.
- every contact leaves a trace

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2
Q

What are the different types of forensic evidence?

A

Biological, physical, and impression evidence

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3
Q

What are the different lights in visual screening?

A

Sunlight
White light / torch
Oblique light

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4
Q

What does oblique light help show in visual screening?

A

Invisible evidence - helps fingerprints

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5
Q

What is crime lite?

A

Hand-held, high intensity light source
Filters alter wavelength allowing forensic evidence to be targeted.
Blood, semen, saliva, bone, teeth, hair,
fibres, shoeprints, fingerprints, gunshot
residue and accelerants.

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6
Q

What is the standard wavelength for crime lite and why do we alter wavelength?

A

415-420nm
Different wavelengths for different bodily fluids

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7
Q

What is biological evidence?

A

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

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8
Q

What chemical tests are used for blood?

A

Combur, KM, Luminol

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9
Q

What chemical test is used for saliva?

A

Phadebas

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10
Q

What chemical test is used for semen?

A

ACP

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11
Q

What happens during a COMBUR test?

A

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

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12
Q

What happens during a KASTLE MEYER test?

A

Phenolphthalein is used to detect possible presence of haemoglobin
Colour change to pink
Less sensitive but more specific - false negative can arise

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13
Q

How is COMBUR test taken?

A

Add water, apply to evidence, turn green if Hb present - some other things will do

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14
Q

What happens during luminol test?

A

Reacts with iron in haemoglobin causing luminescence.

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15
Q

What blood test is done last and why?

A

Luminol
Last test due to mess and disruptive - clean up marks

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16
Q

What substances other than blood may react to luminol test?

A

Bleach, copper and horseradish.

17
Q

What happens during PHADEBAS test?

A

Phadebas Test reacts to α-amylasemby releasing a blue dye.
Presumptive test indicating saliva may be present (amylase is found in other body fluids at lower levels).

18
Q

What happens during ACP test?

A

Suspect stain is sampled by swab or damp blotting paper and a solution (sodium alphanapthylphosphate and fast blue B) is applied.
Purple-blue colouration if positive.

19
Q

What are criteria for collecting biological evidence?

A

Risk Assessment
PPE – gloves and mask(minimum)
Records – photos and notes
Use sterilised/sterile equipment

20
Q

How do we collect blood as biological evidence?

A

One wet swab using sterile water

21
Q

How do we collect saliva as biological evidence?

A

Two swabs – one wet then one dry

22
Q

How do we collect trace/touch as biological evidence?

A

Two swabs – one wet then one dry

23
Q

How do we collect cigarette butt as biological evidence?

A

Entire item into envelope/plastic pottle

24
Q

How do we collect cigarette butt as biological evidence?

A

Entire item into paper bag

25
Q

What is physical evidence?

A

Physical, microscopic and chemical evidence.
Tangible items which can be collected from a crime scene.

26
Q

What are examples of physical evidence?

A

Glass
Paint
Fibres
Soil and Pollen
Hydrocarbons
Gunshot residue
Explosives

27
Q

What is physical fit?

A

Pieces left at a scene can be linked back to the source
Physically fitting the pieces back together
Like a jigsaw puzzle

28
Q

How can glass fragments be linked back to source?

A

Refractive index
Density
Thickness
Colour
Physical fit

29
Q

What are collection considerations when collecting glass?

A

Backscatter ~ 30%
Persistence ~ 24hrs

30
Q

What are packaging considerations when collecting glass?

A

Sharp
Can pierce paper - container

31
Q

What is the glass compared too?

A

Control samples
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

32
Q

When might paint be left?

A

Hit and run
Ram raid
Assault with painted object
Burglary

33
Q

How is paint transfer linked back to source?

A

Layers
Colours
Microscopy
Physical fit

34
Q

What is the paint compared to?

A

Control samples
From damaged panel
Away from the area of damage
Multiple samples
All layers, down to the base

35
Q

What is impression evidence?

A

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

36
Q

What are tool marks in impression evidence?

A

Created when a tool is used to force open a window or door.
A mark will be left on the softer surface.
Burglary

37
Q

Why is toolmark compared to tool microscopically?

A

To identify:
Class characteristics
Individualising characteristics

38
Q

What are class characteristics for toolmarks?

A

No damage
Original condition
Type and size of tool used

FORB201 (7 decks)

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