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Forensic Medicine > Trace Evidence > Flashcards

Trace Evidence Flashcards

1
Q

Describe Locard’s exchange principle

A

Suggests that every contact leaves a trace
Includes things like fingerprints, blood, hair, clothes fibres, tool marks, scratches, semen etc.
Also tells us that physical evidence cannot be wrong, it can only be missed through human error

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2
Q

Where might you find trace evidence

A

At Scene
On Clothing
On Victim - and in their injuries
On Suspect - on their clothing or person
On personnel involved in scene or transfer - paramedics,
police, scientists, forensic Nurse, FME, pathologist, PF

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3
Q

Anyone who attends a crime scene can be involved in the transfer of trace evidence - true or false

A

True
Even without noticing you can contaminate the scene or be contaminated (e.g. leave a hair, pick up a fibre etc.)
Must be aware of all personal at the scene and beyond
This is why hair nets, white suits are used

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4
Q

At it’s simplest, which 3 objects will trace evidence be passed between at a crime scene

A

Evidence from the scene itself
The body/victim
And the assailant

Doesn’t happen in practice - anyone else in contact with scene may then transfer evidence

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5
Q

Which trace evidence would you look for on clothing

A 
Hairs
Fibres
Glass fragments 
Paint - flakes or smears 
GS residues 
Vegetation or pollens - outdoor crime scenes
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6
Q

Which clothing stains may be analysed in criminal cases

A

Blood
Semen - sexual cases
Vomit - analysis of stomach content, especially drugs
Mud / soil - gives a lot of info about location of crime/whether they’ve been moved

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7
Q

How can damage to clothing be useful in criminal cases

A

Cuts, stabs - sharp force
Tears - blunt force
Location and extent of damage can be evidence

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8
Q

How can pollen analysis be used in criminal cases

A

Can tell you where someone has been and when they were there
Very specific shapes/sizes that can be analysed down microscope - resitant particles

Different locations will have different plants and therefore different types of pollen - can identify location

Pollen also has both diurnal and seasonal variations which indicates timings

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9
Q

How can paint flakes be analysed

A

They often have laminated (multi-layered structure) that can be viewed under a microscope
This makes it more unique and allows you to match it to a suspect source
Layer structure can be very specific for identifying cars - can sometimes date a paint chip and match to a specific vehicle (make, model, year)

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10
Q

Is Locard’s principle still relevant to modern forensic medicine

A

YES

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11
Q

Where are glass fragments often found

A

Can get tangled in the hair

Combed out by pathologist and sent for analysis

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12
Q

How can glass fragments be analysed

A

Look at their refractive index, density etc.

These properties can be matched to suspect vehicle/location etc.

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13
Q

Pink stained vomit suggests what

A

Amitriptyline overdose

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14
Q

Clothing searches are routine at autopsy - true or false

A

True

Done whether the death is natural or unnatural

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15
Q

Why must you be careful when searching a victims clothes

A

May have weapons or sharps on them

Particualrly drug abusers - risk of needlestick injury/infections

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16
Q

What is meant by Jigsaw evidence

A

When you can physically match broken pieces of evidence to the scene/substance
Anything that’s torn or broken can be physically put back together to show they had the same origin

Very powerful evidence

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17
Q

List examples of Jigsaw evidence (physical matching)

A

Plastic - RTA (number plate etc.)
Metal - from a car or tool, tip of knife (if left in body can be matched to suspect weapon)
Paper or tape when torn
Anything breakable!

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18
Q

How does velocity affect blood splatter

A

The droplets decrease in size as the velocity increases
Can go from large droplets/pools to a fine mist
The smaller the droplets the less distance they can travel

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19
Q

What can cause a low velocity blood splatter

A

May be dripping from body, thrown off weapon splashed or spurts of arterial blood

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20
Q

What can cause a medium velocity blood splatter

A

Assault with a weapon such as a baseball bat

Striking a ‘pool’ of blood with great force

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21
Q

What can cause a high velocity blood splatter

A

Gunshots

High speed machinery

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22
Q

What would cause a fine mist of blood

A

A high velocity injury/trauma such as a gunshot wound

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23
Q

What can happen to blood after it has splattered

A

Can be transferred or smeared onto other objects

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24
Q

How is leuco malachite green used at crime scenes

A

It is a on-scene test used to indicate the presence of blood
Filter paper has LMG chemicals added and is then touched to a suspect area
If it turns green on contact it means blood is present
Non-destructive chemical test (don’t need to dissolve out the blood)

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25
Q

How can blood splatter distribution be analysed

A

Can look at the length/width of the stains - if you use this to make a ratio you can determine the angle/height it struck the surface

Will also have a direction to then - can draw lines to show their point of origin

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26
Q

Long and thin blood splatters suggest what

A

That the blood has struck the surface at a shallow angle

Can be used to estimate location of source

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27
Q

Short and fat blood splatters suggest what

A

That the blood has struck the surface at a less shallow angle
Can be used to estimate location of source

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28
Q

What is the typical splatter pattern of an arterial bleed

A

Will be pulsatile - up and down and up and down

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29
Q

Which non-intimate samples can be taken on arrest

A

Fingerprints, palm prints, other impressions

Photographs - of suspect

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30
Q

Which non-intimate samples can be taken on arrest as long as the inspector gives permission (i.e. reasonable force)

A

Body hair, other than pubic
Finger or toe-nail clippings or other material from nails
Blood or other body tissues or fluid gained by swabbing or rubbing - not a needle test
Saliva that can be swabbed from the inside of the mouth

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31
Q

Which non-intimate sample requires a warrant

A

A blood sample

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32
Q

Do police have the power to carry out DNA tests

A

Yes
Upon detention or arrest, police can carry out a DNA test
Cells scraped/swabbed from inner cheek lining

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33
Q

What are the 6 main benefits of the National DNA database

A 
Early identification of linked cases (serial crimes)
Early arrest of offenders
Valuable intelligence
Early exoneration of innocent suspects
Easier identification of bodies
Deterrence
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34
Q

What is the purpose of the National DNA Database

A

Holds DNA profiles from those arrested for charged with, informed they will be reported for, or convicted of a recordable offence (e.g. not a minor offence)
Also holds DNA profiles obtained from crime scenes - allows those arrested to be matched to past crimes

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35
Q

Who manages the National DNA database

A

the Forensic Science Service on behalf of the police

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36
Q

What happens to stored DNA, prints etc. if the suspect is convicted

A

They are retained on police files

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37
Q

What happens to stored DNA, prints etc. if the suspect is not convicted

A

They must be destroyed

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38
Q

What happens to stored DNA, prints etc. if the suspect is given an alternative to prosecution such as a fine or work order

A

They can be held for up to 2 years
Even 3 if it was a violent or sexual crime
After this it is destroyed

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39
Q

How long can police store DNA, prints etc. from a suspect in a violent or sexual crime

A

Up to 3 years
Even if they are acquitted or the case dropped
Police can also apply for an extension, to enable retention of DNA information for further periods of up to 2 years at a time

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40
Q

What is required for an intimate sample to be taken

A

Requires consent from the person and a Dr

Police cannot take them

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41
Q

List examples of intimate samples

A 
Blood - taken via venipuncture 
Semen
Any other tissue fluid
Urine 
Pubic hair
Dental impression
Swab from body orifice other than the mouth (vagina, anus)
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42
Q

Can an intimate sample ever be taken without consent

A

Technically yes
Can be taken on the authority of an Inspector from a person in police detention if there are reasonable grounds for suspecting the involvement of the person in a recordable offence and for believing the sample will tend to confirm or disprove his/her involvement

However, most Drs would decline to take it as the GMC and defence unions would not back them

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43
Q

List potential sources of DNA

A 
Blood
Tissue
Semen - one of the best 
Saliva -contains cheek cells
Hair follicles - not just the shaft 
Weapon
Bullet (exited)
Condom
Fingernail scrapings - if victim has scratched attacker
Bite mark - can swab to recover perpetrator DNA 
Glass / bottle - drank from or inserted 
Cigarette - saliva on butt
Stamp - if licked will have saliva/cells on it 
Dandruff
Fingerprints
Clothing, hat - cells found in these
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44
Q

Which part of the hair can you get DNA from

A

Only the follicle

Can’t get DNA from shaft only

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45
Q

Why is a condom such a good source of DNA

A

Will have victims DNA on outside (vaginal or anal cells) and assailant on inside (sperm)

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46
Q

Why is semen such a good source of evidence

A

Contains loads to DNA specific to individual - head of sperm cells are packed with paternal DNA
Also contains AP and PSA which can be used in analysis

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47
Q

How might you find victim’s DNA on the male suspect following a sexual assault

A

Vaginal cells containing victim’s DNA rubs off onto penis

This can persist for around 24hrs and even transfer into the perpetrators underwear

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48
Q

What are the main components of semen

A

Sperm - come from testes, around 20-100 million per ejaculate

Seminal fluid - mixture of fluids from the prostate and seminal vesicles

Forms a whitish fluid with a pH of 7.2-8

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49
Q

How much semen is produced per ejaculate

A

Around 2-6ml

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50
Q

What happens to sperm motility as time progresses

A

It decreases

There is rapid progression within 60 minutes of ejaculation

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51
Q

What are the most important constituents of semen in terms of analysis

A

Spermatozoa (from testes)
Acid Phosphatase (from prostate)
Prostatic Specific Antigen P30 (from prostate)
Choline, Spermine

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52
Q

Describe the appearance of semen immediately after ejaculation

A

Sticky, jelly-like liquid often forming globules

Usually white in colour, but may appear grey or even yellowish

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53
Q

Why might semen appear pink

A

Blood in the semen (hematospermia) can cause a pink or reddish colour

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54
Q

Describe the appearance of semen between 5-40 mins after ejaculation

A

It becomes more watery and liquid before finally drying in

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55
Q

How is semen detected at a crime scene

A

It will fluoresce under UV light - can scan scene with light

May also look for a dry, crusty stain - more likely than fresh sample at scene

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56
Q

How long do sperm survive post ejaculation

A 
Motile sperm only live up to 4-6 hours in the vaginal canal
Intact sperm (with tails) not usually found after 16 hours  but have been found up to 72 hours in the GU tract
Non motile sperm (no tails) normally found in upper vagina up to 3 days after intercourse, and sometimes up to 6 days or later in the cervix.
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57
Q

How does the pH of the vagina affect sperm motility

A

Acidic environment of the vagina decreases motile sperm count rapidly

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58
Q

How can sperm be lost

A

Dilution -by vaginal secretions, saliva
Drainage -under gravity, from vagina to/from anus
Degradation (seminal enzymes, loss of tails)
Defecation - flushes out anal sperm
Victim may wash or drink (dilutes)

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59
Q

How does semen typically drain from the vagina

A

Most commonly drains from the vagina down to the anus if lying on back (with gravity)

Vaginal contamination from anal semen deposits is rarer but can be seen

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60
Q

Why should samples be taken ASAP in sexual assault cases

A

Prevents the loss of semen samples

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61
Q

How long do sperm survive in the mouth

A

<6-12 hours

Swab up to 2 days just in case

62
Q

How long do sperm survive in the upper vagina

A

Motile spermatozoa: <6-12 hours
Non-motile (tails lost): < 3 – 6 days
Acid phosphatase < 48 hours

Swab up to 7 days just in case

63
Q

How long do sperm survive in the endocervical canal

A

Up to 7-10 days

The higher the get the better they survive - less likely to drain/be lost

64
Q

How long do sperm survive in the anus

A

Less than 2 days

65
Q

How long do sperm survive in the rectum

A

Less than 3 days
The higher the get the better they survive - less likely to drain/be lost
Swab up to 3 days just in case

66
Q

What is involved in the examination of sexual assault victim or suspect

A

History - what’s happened, where
Clothing - taken for analysis (hair, semen, tears)
General Examination - injuries, evidence etc.
Genital Examination - injuries and take swabs
Blood sample

67
Q

What is looked for/taken on general examination is sexual assault cases

A 
Injuries etc.
Hair (combed & Cut)
Mouth Swabs
Skin swabs
Fingernail scrapings
68
Q

What is looked for/taken on genital examination is sexual assault cases

A 
Injuries etc.
Pubic hair (combed & cut)
Vaginal swabs (vulva, low vagina, upper vagina)
Anal swabs (perianal, anal canal & rectum)
69
Q

Describe the double swab technique

A

First, moistened swab rolled over skin
This rehydrates & loosens foreign cells

Second, dry swab rolled over same area
Picks up foreign cells

70
Q

Why is the double swab technique used

A

Has a higher recovery of cells and DNA than single swab

71
Q

Where is the double swab technique used

A

On the skin - particularly bite marks
On vulva
Perianal skin
On penis

72
Q

Which lab samples are taken from a victim of sexual assault and in which order

A 
Clothing
Head hair (combed, cut & plucked)‏
Swabs from mouth, saliva (<2 d)
Fingernail scrapings, clippings and/or swabs 
Skin swabs from bites (moist + dry)
Pubic hair (combed & cut)‏
Vaginal Swabs- taken up to 7 days post assault 
Ano-rectal swabs 
Blood
73
Q

Are hairs plucked from living victims for analysis

A

Not typically

Usually comb and cut hair in the living and comb then pluck hairs from dead victims

74
Q

Where are vaginal swabs taken from in sexual assault cases

A

Vulva (moist + dry swab)
Lower 1/3 at 3-5 cm (2 dry swabs as already moist)
Upper 2/3 after insertion of speculum (2 dry)
Endocervical canal (2 dry)

75
Q

How are fingernails swabbed

A

A moist and then dry rolled over nail bed and edge

Use one set for each hand

76
Q

Why are speculums used for high vaginal swabs

A

To prevent you touching the lower vaginal as this will contaminate the sample

77
Q

Endocervical swabs can be taken from above post mortem - true or false

A

True

In life you need a speculum exam

78
Q

Which intimate swab is taken first - anal or vaginal

A

Vaginal

79
Q

From which regions are ano-rectal swabs taken

A

Perianal skin -3 cm radius from anus (1 moist + 1 dry)
Anal canal- gentle rotation at 2-3 cm (2 dry)
Rectum, after insertion of proctoscope to prevent anal contamination >4 cm (2 dry)

80
Q

How long after assault can ano-rectal swabs be taken

A

Up to 3 days

81
Q

How long after assault can vaginal swabs be taken

A

Up to 7 days for vaginal intercourse

Within 12 hours for digital penetration

82
Q

Intimate swabs are taken from inside to outside - true or false

A

False

Taken from outside skin to internally - prevents contamination by pushing samples further in

83
Q

Which swabs are taken from the penis of the suspect in sexual assault cases

A

Shaft (moist + dry)
Foreskin / Coronal Sulcus (moist + dry)
Glans - pull foreskin back (moist + dry)

84
Q

Which swabs are taken from the suspect in sexual assault cases and in which order

A 
Clothing
Head hair (combed & cut)‏
Fingernail scrapings, clippings &/or swabs 
Pubic hair (combed & cut)‏
Swabs from penis 
Blood, Saliva
85
Q

How long after a sexual assault can swabs be taken from the penis

A

Up to 3 days

86
Q

How are mouth swabs taken

A

2 Dry swabs rubbed over & under tongue, over all sides of teeth and gums and inside cheeks

Mouth rinse with sterile water into polypot - done in the police early intervention kit
Collects cells by rinsing saliva sample

87
Q

How long after oral penetration can swabs be taken

A

Within 2 days

88
Q

Why is a mouth sample taken in the police early intervention kit

A

Semen only lasts a few hours in mouth so must be taken quickly

89
Q

Name the vaginal swabs taken after sexual assault

A

Vulva
Low Vagina
High vagina
Cervical canal

Sometimes do introitus but rarer

90
Q

Name the anal swabs taken after sexual assault

A

Perianal
Anal canal
Rectum

Also have the anal margin and internal anal but not routinely taken

91
Q

How are specimens labelled as evidence in criminal cases

A 
Name of subject
Type of specimen
Date & time collected
Place collected - e.g. scene or mortuary 
Name of collector (FME or nurse)
Name of witness (nurse)

Name of police officer to whom it is handed

92
Q

What is the chain of custody

A

It is a legal term that refers to the ability to guarantee the identity and integrity of the specimen from collection through to reporting of the test results

It is the process used to maintain and document the chronological history of the specimen

93
Q

Chain of custody documents should contain what information

A

Name or initials of the individual collecting the specimen
Each person or entity subsequently having custody of it
The date the specimen was collected or transferred
Specimen type
Patient’s name,
Brief description of the specimen

94
Q

What is the benefit of a secure chain of custody

A

When combined with good analytic techniques in the lab it leads to the production of a legally defensible report.

Needs to be a clean, concise process

95
Q

What is demonstrated by the chain of custody

A 
Collection of the correct item
From the correct person
Transported
correctly 
Stored correctly 
No interference
No addition
No loss
No contamination
96
Q

Give an example of a typical chain of custody

A

Samples from the victim/suspect is take by a FME or a forensic nurse
This is then handed to the police who transfer it to the scientist in the forensic lab
Results are given back to the police and eventually court

97
Q

How are vaginal swabs processed in the lab

A

The material on the bud of the swab extracted by soaking in 1ml of distilled water
Centrifuge
The supernatant removed to another tube
The cell pellet re-suspended in more distilled water and then dropped on a slide
It is heat fixed and can be stained or tested for various compounds - sperm, AP etc

98
Q

How is sperm detected in the lab

A

Microscopy is diagnostic

Look for sperm themselves in the sample

99
Q

How is acid phosphatase analysed in the lab

A

There are chemical tests that allow it’s detection

100
Q

Is acid phosphatase specific for semen

A

No - it is not specific

Gives false positives

101
Q

How is prostate specific antigen analysed in the lab

A

There are immunological tests for it
Can be done with antibodies from rabbits, by gel electrophoresis with AB-Ag precipitation or by more modern dye tests which are more specific

102
Q

What is acid phosphatase

A

Enzyme from prostate gland
Found at high concentrations in the semen (400x higher than elsewhere)

Low concentration in vaginal secretions & other bodily fluids

103
Q

For how long is acid phosphatase detectable

A

Up to 48hrs

104
Q

How can you test for acid phosphatase

A

There is a colour test - can be done as a field test (filter paper with chemicals)
If it turns purple in under 30s it is positive
Can be done on clothing and other material

105
Q

What is Prostatic Specific Antigen

A

It is a glycoprotein that is specific to the prostate gland in males - produced there
It is secreted into the seminal fluid - one of the major proteins

106
Q

What is the function of PSA

A

To liquefy the seminal fluid

107
Q

High conc. PSA a useful forensic marker for the detection of seminal fluid - true or false

A

True

Useful for even small amounts

108
Q

What are the advantages of testing for PSA

A

Accepted marker for semen in criminal cases.
PSA test is not presumptive like Acid Phosphatase
Detection possible in cases where sperm cannot be found
Can be recovered from samples up to 30 years old
Can be detected even if semen is very dilute
Detectable in post-ejaculate urine

109
Q

Why might sperm not be found in a semen sample

A

If the man has had a vasectomy - cut vas deferens (will also miss the seminal vesicle fluids)
If they are azoospermic

Will also see AP

110
Q

Can you identify an individual from AP or PSA

A

No
Not identifiable
Just tells you it’s semen

111
Q

When is a vasectomy considered successful

A

Once the sperm count is zero

Checked for with follow up sperm count tests

112
Q

How would you test for semen in men who have had vasectomies

A

Cant test for sperm so have to employ different tests such as AP and PSA

113
Q

Where might you get mud/soil samples from

A

Clothing
Footwear
Tyres

May also leave print in mud that can be matched (2 way transfer)

114
Q

How can mud/soil samples be analysed

A

Look at the colour when dried
Assess particle size/density
Mineral Composition
Biological composition (plants, pollens, microbiology -bacteria etc)

Can help identify location

115
Q

Mud/soil samples may be important parts of sexual crime scenes - true or false

A

True

If victim was dragged across ground or pinned down

116
Q

What is palynology

A

The analysis of plant pollens

Fairly new science but becoming more important in forensics

117
Q

Where can pollen samples be taken from

A

Soil
Cars: tyres, wheel arches (thrown up in mud), upholstery (from person)
Hair, clothes and shoes
Under fingernails
Nasal cavities, gut - inhaled or swallowed
Firearms
Other substances: drug packages, explosives

118
Q

What is the most common type of trace evidence encountered

A

Fibres

Found in may crimes and can provide critical evidence

119
Q

Can you individualize fibres

A

Not usually

Especially due to mass production

120
Q

Describe primary, secondary and tertiary fibre transfer

A

Primary - from scene to person (A-B)
Secondary (A- C via B) - e.g. sit somewhere transfer fibres from different surfaces
Tertiary - fibres transferred from scene to person to another person via a common surface

121
Q

which natural fibres may you find at a crime scene

A

Animal fibres (protein):
Silk (fibroin)
Wool (keratin)
Hair (keratin)

Vegetable fibres (cellulose):
Seed fibres
Stem fibres
Leaf fibres

Mineral fibres (asbestos)

122
Q

which artificial fibres may you find at a crime scene

A

Regenerated fibres which are manufactured from natural raw materials
- e.g. rayon, acetate

Synthetic fibres which are produced from synthetic chemicals
- e.g. nylons, polyesters, acrylics
becoming more common

123
Q

Describe the different mechanisms of fibre transfer

A

Whole or fragmented fibres that lie loosely on the surface may be shed

Whole or fragmented fibres may be embedded in material and may be pulled out or shed

Fibre may break due to stress and a piece of the fibre may then be shed

124
Q

How are fibres examined in the lab

A

Microscopy - normal light, polarised, UV, comparison
IR Spectroscopy
Dye type (chromatography)

Incidence (how common is it) and number analysed
Newer, synthetic fibres are more useful as easier to identify

125
Q

The more fibre tests you can do the more sure you can be that they are a match - true or false

A

True
Need to make sure that no test can distinguish them

As soon as they become distinguishable they are no longer a match

126
Q

What can you ascertain from a hair sample

A

Species
Sex
Site
Identify the individual via DNA if you have the follicle

127
Q

Where are hair fibres often found

A

On weapons
On windscreens following a RTA
Often stuck in blood - good glue for fibres

128
Q

Hair fibres are common evidence in which types of crime

A

Assault

Sexual assault

129
Q

Describe the structure of the hair follicle

A

Forms the base of the hair - root is attached here initially
Has blood supply, muscles and sebaceous glands

130
Q

Describe the phases of hair development

A

Anagen phase - growth phase, present 80-90% of time

Catagen phase - slow growth/resting

Telogen phase - hair pushed out of follicle then shed

131
Q

Describe the structure of the hair cuticle

A

Overlapping scales of keratin

Pattern indicates species

132
Q

Describe the structure of the hair cortex

A

Has parallel spindle cells in regular parallel array

Also has pigment granules (colour, shape & distribution important)

133
Q

Describe the structure of the hair medulla

A

Central cylindrical canal
Pigment pattern can be continuous, Interrupted, Fragmented, Absent
In humans they are absent or interrupted but can be inter/intra individual variation - used to identify species and some other useful factors such as race

134
Q

What is the medullary index and why is it useful in hair analysis

A

It is the ratio of medulla to cortex in a hair strand

Can be used to help identify source - e.g. if less than 1/3 it is likely human

135
Q

What can the morphology of hair fibre scales, cortex, medulla tell us

A 
The species 
Body area
Racial origin
Age
Sex 
Whether they have bleached/dyed their hair
136
Q

How can you tell if the hair has been forcibly removed

A

Sheath cells will also be present in the sample

137
Q

Can you identify a suspect through hair sample comparison

A

Not reliably

138
Q

How can you tell which direction glass was broken from

A

You analyse the stress marks (Wallner Lines) along the broken edges

Radial cracks have Ridges at Right angles to the Rear face
Concentric cracks have ridges at right angles to front face

139
Q

What is a radial glass fracture

A

Cracks which radiate out from the point of impact on glass

Will have Ridges at Right angles to the Rear face

140
Q

What is a concentric glass fracture

A

Form a spider web pattern around a circular centre

Will have ridges at right angles to front face

141
Q

How does tempered glass break

A

It tends to shatter on impact

Designed this way for safety - e.g. side windows of cars (if an occupant impacts it the energy is dispersed)

142
Q

Describe the glass structure of car windscreens

A

They are usually laminated - have plastic in between 2 layers of tempered glass

Will shatter on impact to disperse energy but the plastic will keep occupants in the car

143
Q

What happens to glass when struck by a bullet

A

Creates a massive fragmentation pattern - both forwards and backwards
Will have fragments on both sides - present on victim and shooter

144
Q

What is meant by a toolmark

A

Any impression, gouge, cut, scrape made by hard object into a softer surface
Will leave behind damage

145
Q

What is a 3D toolmark called

A

Impression

146
Q

What is a 2D toolmark called

A

Striation

Caused by linear scratching of surface

147
Q

What identifiable features may you get from a toolmark

A

Class characteristics - general grouping such as type, size or shape

Individual characteristics - unique marks due to random wear or damage of individual tool
Can be transient and change or may be permanent

148
Q

In which substances would footwear or tyres leave 3D impressions

A

Soft materials such as mud, sand or snow

149
Q

In which substances would footwear or tyres leave 2D prints

A

Left on harder surfaces in substances like blood, dirt or dust

150
Q

What identifiable features may you get from footwear or tyre marks

A

Class Characteristics - general grouping such as manufacturer, type, size, shape etc.

Individual Characteristics - Unique identifying features due to random wear & damage
E.g. glass, nails, stones trapped in tread or a wear pattern
Transient or permanent

Forensic Medicine (13 decks)

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