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2Y Study > 5 - Forensics > Flashcards

5 - Forensics Flashcards

1
Q

What is Locard’s Principle?

A

Every contact leaves a trace.

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2
Q

What is the Physical Fit principle?

A

Can prove beyond reasonable doubt the connection between a crime scene and suspect - e.g. can the glass from a window be traced back?

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3
Q

What is trace evidence and give examples.

A

These are small amounts of material which could be skin cells, DNA, blood, hair, fibres, soil, plant material etc.

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4
Q

What are the two types of trace evidence?

A
  1. Inceptive - found a trace and follow it
  2. Reactive - given specific detail/lead so try to find traces to support it at scene.
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5
Q

What four factors affect trace evidence?

A
  1. Amount
  2. Persistence
  3. Finding the material
  4. Evidence value (rare?)
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6
Q

Give some methods of trace evidence recovery.

A

Shaking, brushing, taping, vacuuming, swabbing, hand picking/tweezers. extracting and pipette/swab.

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7
Q

How do you analyse:
(a) glass
(b) fibres - hair
(c) semen
(d) saliva
(e) blood

A

(a) colour, thickness, physical and chemical analysis. Physical fit - bullet hole direction etc.
(b) commonality, man-made/natural. Hair - cuticle, cortex and medulla, source of hairs, limited evidential value.
(c) enzyme testing (acid phosphatase), p30 (present even when sterile).
(d) may contain bacterial/cheek cells, starch/iodine test - black would disappear.
(e) preliminary tests not entirely specific so false reactions can occur, stains absent after cleaning, haemoglobin enzyme/catalyst used to test reactions, RBS and platelets lack DNA.

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8
Q

What are the three blood tests we can use for the reaction between haemoglobin and hydrogen peroxide if there is no clear evidence?

A
  1. Leuchomalachite green (LMG) - oxidised turns green.
  2. Kastle Meyer - phenolphthalein turns pink if oxidised.
  3. Luminol - shows chemiluminescence in presence of Hb - product is 3-aminophthalate and will show blue.
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9
Q

What are the four blood pattern types?

A
  1. Passive - gravity, drips, pools - affected by target surface.
  2. Transfer - blood from one surface comes in contact with another.
  3. Projected - active blood patterns like arterial spurts or cast off stains.
  4. Void - shows furniture or victim was once there.
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10
Q

What is the significance and reliability of evidence?

A

Significance - rarity, expectations, combination, extent of comparison, contamination etc.
Reliability - reputable, relevant funding etc.

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11
Q

What are the five factors affecting alcohol absorption?

A
  1. Quantity
  2. Concentration
  3. Contact time in GIT
  4. Food
  5. Stomach emptying
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12
Q

How does alcohol distribute through the body?

A

The distribution is rapid and goes to all organs and body compartments proportionate to water content/levels.

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13
Q

How is alcohol cleared from the body (2)?

A
  1. Nausea is a self-protective mechanism as it gets ride of alcohol contents and reduced volume being absorbed.
  2. > 90% is metabolised and goes via liver, converting ethanol into acetaldehyde, then into CO2 and water. This process reduces BAC by ~18mg/100ml/hour.
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14
Q

How is harm caused by alcohol to the body and how does it differ in individuals?

A

Alcohol dehydrogenase (ADH) breaks acetaldehyde into acetate, which enter circulation, and free radicals are produced from conversion of NAD+ to NADH - damages tissues.
It differs between people due to genetics as we have many variations of ADH so we vary from fast to slow metabolism - e.g. ADH1B*2 = fast.

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15
Q

At what rate is alcohol cleared from the body?

A

It is cleared at a constant rate so is dependent on liver size and body mass, but independent of concentration and amount.

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16
Q

What is the legal limit of BAC for driving in Scotland and why?

A

50mg/100ml as this level begins to impact coordination.

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17
Q

Why do limits change depending on source?

A

We must take into account the varying concentrations that occur - like urine will tend to have higher levels in samples.

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18
Q

What is the most accurate measurement of alcohol concentration and why?

A

Blood - concentration affects the brain due to the rapid equilibrium across the blood brain barrier.

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19
Q

What is urine and breath alcohol concentration like?

A

Urine - provides mean value over period of secretion.
Breath - in equilibrium with blood but in smaller concentrations.

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20
Q

What is the least accurate methods of measuring alcohol concentration?

A

Measuring amount of reduce co-enzyme present in sample calorimetrically and spectrophotometrically - ADH in presence of co-enzyme will oxidise alcohol.

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21
Q

How does a roadside breathalyser work?

A

A positive charge passes with alcohol through the chambers, giving an indication of BAC - conversion of breath from % given.

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22
Q

What is the time calculation for BAC?

A

Tmax (time at which alcohol content is at its max) = Cmax - (t*elimination rate)

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23
Q

What is Paracelsus’s third defence?

A

The potential of the quantity - it is solely the dose that determines that a thing is not poison.

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24
Q

How are drugs organised and categorised?

A

Organised into classes A-C and temporary (legal highs, synthetic versions which act in similar ways).
Categorised by impact.
Temporary can be more lethal - can be banned for one year to be classified.
Sentences vary on class and extent.

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25
Q

What is a stimulant and give two examples.

A

Primarily stimulates brain activity (via prefrontal cortex).
Increase dopamine.
E.g. amphetamines and cocaine.

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26
Q

What is a depressant and give four examples.

A

Primarily inhibits brain activity (via neuronal and synaptic activity).
E.g. alcohol, barbiturates, benzodiazepines, and heroin.

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27
Q

What are hallucinogens and give three examples.

A

Induces alterations in perception and mood (targets limbic area).
E.g. Ecstasy, lysergic acid diethylamide (LSD), and cannabis.

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28
Q

What does the analysis of drugs allow for/is (3)?

A
  1. Track production (bulk/trace)
  2. Can be qualitative or quantitative
  3. Can be chronic or acute - cause of accidents.
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29
Q

What are the two main ways we can perform analysis?

A
  1. Presumptive tests - gives idea that there may be drugs present e.g. colour change.
  2. Chromatography - separates out components - spikes based on weight etc, and each drug has unique signature for identification.
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30
Q

Describe hair analysis.

A

Hair traps and retains substances in the shaft over a prolonged period of time due to its slow growth and weak binding to melanin.
It can be analysed by burning - detecting metabolites.

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31
Q

What is the difference between dose and concentration response, and LD50.

A

Concentration - used for experiments in vitro or isolated tissue.
Dose - used when certain amounts are given to a human or animal model.
> LD50 can be measured from dose response curve (lethal dose that will kill 50% of population).

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32
Q

What are the five factors affecting toxicity?

A
  1. LD50
  2. Sensitisation
  3. Tolerance
  4. Accumulation
  5. Bioavailability
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33
Q

Why is blood grouping useful?

A

It is an effective way of eliminating individuals from a large sample pool, and is inexpensive and quick.
It can be used for protein variants and blood-cell related proteins.

34
Q

What are biological markers, and where are antibodies and antigens found?

A

Biological markers - those recognised by antibodies.
Antibodies - in serum
Antigens - in RBC

35
Q

Who can accept O?

A

O is the universal donor so can be accepted by anyone, and has both Anti-A and B in the serum, and AB can accept from anyone due to both A and B antigens on their RBC.

36
Q

What are secretors and non-secretors?

A

Secretor - 75-85% of population, other bodily fluids have similar profile to serum. Your antigen (A/B) on RBCs and free antigens become present in fluids, meaning you can profile blood groups via saliva etc.
Non-secretor - less prone to norovirus, nothing to detect/identify.

37
Q

What are good and bad biological sources (4 each)?

A

Good - WBC, sperm, hair with roots and vaginal fluid.
Bad - urine, hair shaft, skin cells, and faeces - may contain little or degraded cells.

38
Q

Why are skin and RBC bad?

A

Skin - constantly shed so have already undergone damage, so instead use cheek.
RBC - lack DNA due to no nucleus.

39
Q

Give marker types (3) and their source of variation (4).

A
  1. from nucleus:
    a - Autosomes - STRs (all, high discrim, very degraded difficult to type) or SNPs (all but low mutation, usable on degraded, low discrim, mixtures tricky)
    b - Y chromosome - STRs (mutation, male-specific, good for mixtures, low discrim).
  2. mtDNA
    a. Control region - SNPs (mutation only, matriline, high copy number, good survival, low discrim).
40
Q

How can we differentiate between identical twins DNA profiles?

A

Using methylation profiles (same genomic and mtDNA) as this varies with gut microbiome, diet, environment, stresses etc.

41
Q

Explain restriction fragment length polymorphism (RLFP) analysis.

A
  • Relies on VNTRs
  • Visualise lengths via cutting and gel electrophoresis
  • Requires DNA which will run well (not degraded)
42
Q

Explain PCR of STRs and one risk.

A
  • Less DNA used and can be partially degraded.
  • Issue: slippage - when polymerase falls off and misaligns, meaning more or less copies of an STR made.
43
Q

What is SNP analysis?

A

Identifies whether an individual has one variant or another at a certain locus.

44
Q

Describe mtDNA.

A

One mitochondrion has 5-10 identical circular molecules of DNA, which is useful for identifying whether individuals belong in the same family - first identification pass.

45
Q

What is Y chromosome testing?

A

The amelogenin locus is on X and Y and has a specific deletion absent on Y, but present on X, so they differ in size - Y is smaller. This allows us to identify DNA mixtures based on peak sizes.

46
Q

What are DNA matches based on and what can the results show for forensic cases (3)?

A

It is solely based on probabilities (should be sufficient sites to distinguish profiles). DNA matches can be used for exclusion, inclusion or can be inconclusive.

47
Q

How do you calculate overall probabilty?

A

Calculate all probabilities separately as before and then multiply them together.

48
Q

Give reasons for why a DNA profile match is not 100% accurate and so cannot be used in court (5).

A
  1. Degraded DNA (incorrect STR number amplified)
  2. Human error
  3. Technical error
  4. Contamination
  5. PCR stutter (slippage)
49
Q

Describe analysis of LCN DNA (low copy number).

A

There is little to work with and amplify, but can result in the same discriminatory power as normal routine DNA profiling. It takes longer and creates a partial profile.

50
Q

What is a partial profile?

A

Can be used for familial searching, and prioritise using specific parameters via location etc. It is never exact, we are looking for patterns.

51
Q

What is familial searching?

A

If you have a full DNA profile but no match, you can look for similar profiles (family), or partial matches. Markers can be used like age, ethnicity etc.

52
Q

What are cold cases?

A

These are severe crimes which occurred decades ago, where the leads dried up after intense investigation due to insufficient evidence.

53
Q

What is DNA boost?

A

This is a computer-based analysis system that interprets DNA mixtures and can be used for mtDNA matches, cold cases etc.

54
Q

What new methods can be used to identify an individual if there is no complete body (4)?

A

If decomposition has occurred, we can use bone extractions, mini STRs, SNPs and mtDNA.

55
Q

How can DNA analysis be used for genetic diseases?

A

Mutations in genes can lead to defects, and genetic diversity can cause polymorphism. It can detect diseases by RFLP or PCR, by amplifying regions that have known causes. We can look at STRs in intergenic regions.

56
Q

What are the two routes DNA analysis can be used for wildlife?

A
  1. Prosecuting trader
  2. Used for conservation or evolutionary analysis - breeding using DNA profiles of species etc.
57
Q

Why may DNA analysis of wildlife have forensic relevance - give examples (5).

A
  1. Cause of injury, death, PM damage
  2. Victim of neglect
  3. Illegal trade/killing of protected species
  4. Poaching
  5. Food spoilage
58
Q

Why is wildlife DNA analysis rarely used?

A

It is costly so only used when necessary for conviction.

59
Q

What are the ethical issues surrounding forensic bioscience?

A

Should we all have our DNA profiles on central databases? - would it make crimes more solvable, or result in framing, invasion of privacy? potential for abuse of profiles?

60
Q

What four things can insects provide that make them of value in forensics?

A
  1. Detect drugs
  2. Detect poisons (ingest when feeding)
  3. Determine location (known habitats)
  4. Finding presence and time of wound inflictions
61
Q

What are the three areas of applications for insects?

A
  1. Insects which inhabit human remains
  2. Insects which damage structures
  3. Infestation of foods
62
Q

What is the post mortem interval (PMI)?

A

The time interval between death and PM exam (discovery).

63
Q

How do insects have an association with forensics and PMI, and what circumstances can we identify (5)?

A

They arrive in set patterns to colonise the body known as succession - this allows us to see the circumstances surrounding death like change in location, body on surface, in contact with water, buried or disturbed.

64
Q

Give 7 reasons why insects are successful in forensics.

A
  1. Metamorphosis - varies with temp.
  2. Feeding strategies.
  3. Sophisticated behaviour - lice leave when body too cold.
  4. Small size.
  5. Chitin - exoskeleton.
  6. Wings.
  7. Life cycles.
65
Q

Give the four forensic indicators for invertebrates.

A
  1. Attracted to dead bodies - detritivores.
  2. Leave dead bodies - lice.
  3. Accidentally associated - trapped in clothing.
  4. Cause of death - anaphylactic reaction.
66
Q

How can we collect insects and what is the issue with maggots?

A
  • Collect via nets and put in collecting pot with appropriate labelling.
  • Specimen jars for maggots.
  • Issue surrounding identification of maggots
    > Keep in lab so we can identify after development
    > Speed up via increase temp
67
Q

Describe the insect colonisation/life cycle of the Blow Fly.

A
  • Females arrive within minutes to lay ~300 eggs in wounds and natural openings.
  • Within 24hrs eggs begin to hatch into 1st instar
  • Feed/moult into 2nd and 3rd
  • Prepupae larvae move away and stop feeding
  • Moult to pupae and final stage of moult to adult
  • Cycle repeats
68
Q

Why are microorganisms key for forensics (3)?

A
  1. Advances in technology
  2. Awareness of dangers of pathogenic microbes
  3. Increase in bioterrorism
69
Q

Why can we not use microbes for PMI?

A

We have an intrinsic link with them as we are constantly hosts to a large number of microbes.

70
Q

How does time before discovery affect PMI?

A

The more time that has passed, the lower the PMI accuracy - estimates are off.

71
Q

Give five factors which increase rate of cooling.

A
  1. Small body
  2. Low fat content
  3. Body stretched out
  4. Lack of clothes
  5. Serious blood loss
72
Q

Give five factors which delay the rate of cooling.

A
  1. Large body
  2. High fat content
  3. Foetal position
  4. Protection from draughts
  5. Insulative coverings
73
Q

What is algor mortis and how can it be used for calculations?

A
  • freezing/cooling of the body
  • internal temp taken and used for calculating hours since death
  • still shows algor mortis if found close to death, and higher accuracy
  • (F - internal)/1.5
74
Q

What is liver mortis/hypostasis?

A
  • blood settles due to gravity, migrating to downwards surface of body
  • identified by pale, white areas called pallor - received most pressure from being in contact with the ground
  • useful for identifying whether body has been moved
  • not useful for PMI
75
Q

What is rigor mortis?

A
  • 3-6 hours after death
  • stiffening of muscles due to less ATP available for contraction
  • evident in small muscles first
  • disappears after 24-36hrs so useful for PMI
  • affected by temp, muscle mass, and PA before death
76
Q

What are the five stages of decomposition?

A
  1. Fresh - body cools, liver/rigor mortis may be seen, blow fly attracted.
  2. Bloat - discolouration, body swells, decay, fluid.
  3. Putrefaction - liquify, blackens, deflates.
  4. Advanced decay - progressive loss of skin/tissue, decay by insects slows, dries.
  5. Dry remains - skin/tissue gone, decay slows, external forces may affect skeleton.
77
Q

What are the four visible features of decomposition in order?

A
  1. Greenish discolouration - breakdown of haemoglobin by intestinal bacteria, first in LR quadrant.
  2. Skin slippage - separation of epidermis from dermis, blistering.
  3. Marbling - same bacteria travels via blood vessels, creating marbling and superficial veins (purple/green).
  4. Bloat/purge - build-up of gas (by-product), ruptures body, foul smell.
78
Q

What is mummification?

A
  • features preserved - no skin would be present has it undergone decomposition
  • desiccation of remains only in hot/cold dry
  • skin dries
  • leathery
79
Q

What is adipocere?

A
  • preserved features
  • grave wax - hydrolysis of body fats
  • seen in bodies partially submerged in water
  • favours damp
80
Q

What is accumulated degree days (ADD) and how do you calculate it?

A

The total temperature or cumulative degrees that the body has been exposed to from death recovery.
We calculate the avg temp on a given day, add the daily temps by day to see which is closest to calculated.

81
Q

What is the total body scoring system (TBS) and how is it calculated?

A

Table are assigned to differing body regions (head, trunk, limbs) and is used to assess which stage of decomposition each region is - qualitative.
Points increase from fresh to dry remains.
Scores add up to give TBS, used to work our how many days it would take to achieve that level of decomposition - based on ADD.

82
Q

In relation to ADD, when will decomposition stop?

A

Decomposition will occur down to 0 degrees due to salt concentrations in the body.

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