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Advanced Forensic Science > Topic 4: CAI Part 2 > Flashcards

Topic 4: CAI Part 2 Flashcards

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1
Q

Evaluative Report

A

Type of report which provides an assessment of the strength to be attached to findings

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2
Q

What must combined probability add up to?

A

One

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3
Q

What is synonymous with transposing the conditional?

A

Prosecutors fallacy

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4
Q

What different types can transfer be?

A

Primary, secondary or teritiary

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5
Q

What is the second part of the transfer process?

A

Persistance

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6
Q

A likelihood ratio between 2 and 10 provides what level of support?

A

A weak level of support

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7
Q

Probability

A
  • Probability (perhaps think likelihood) is a measurement of that event will occur
  • Probability is quantified as a number between zero and one
  • Zero indicates impossibility of the event a occurring
  • One indicates certainty
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8
Q

Rule of Probability #1

A

The probability of any event will always be a number from 0 to 1

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9
Q

Rule of probability #2

A

When an event cannot occur, the probability will be zero

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10
Q

Rule of Probability #3?

A

When an event is certain to occur, the probability is one

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11
Q

Rule of probability #4

A

The sum of the probabilities of all the outcomes in the sample is one

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12
Q

Rule of Probability #5

A

The probability that an event will not occur is equal to 1, minus the probability that the event will occur

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13
Q

What are the two factors required to determine probability?

A
  1. ‘E’ the event whose probability is being considered and
  2. ‘I’ the information available to the assessor when the probability of ‘E’ is being considered
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14
Q

Axiomatic laws of probability

A
  • All the probabilities most add up to 1 (as we’ve discussed previously )
  • The accused is either guilty or innocent (in England and Wales at least)
  • pG (Guilty) + pI (innocent) must equal 1
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15
Q

Probability can be either:

A

Probability can be either:
* Objective - A logical measure of chance where everyone would be expected to agree to the value of the relecant probability
* Subjective - Measuring the strength of a persons belief in a particular proposition

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16
Q

In probability, what does X represent?

A

X represents variable of interest

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17
Q

In probability, what does p represent?

A

P represents the probability of X

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18
Q

The probability that the accused is guilty, in light of the evidence introduced at trial. Typically this is expressed as:

A

The probability that the accused is guilty, in light of the evidence introduced at trial. Typically this is expressed as:
1. p (GIE) or the probability of guilt, given the evidence and
2. p (IIE) or the probability of innocence given the evidence

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19
Q

Lucia De Berk

A
  • Arrested in 2001 after the death of a baby in her care at a hospital in The Hague, apparently from poisoning.
  • Afterwards, investigators found what they thought was a trend of suspicious deaths among 13 patients treated by De Berk in the previous four years. Five others almost died in what investigators said were suspicious circumstances.
  • In 2003, she was convicted of four murders and three attempted murders, and sentenced to life in prison.
  • Part of the evidence against her was the testimony of a statistician, who said the odds were 342 million-to-one that it was a coincidence she had been on duty when all the incidents occurred
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20
Q

What happened in the Lucia De Berk case?

A
  • Initially the death was thought of as natural causes.
  • 30+ suspicious deaths were being investigated
  • The (flawed) logic and only evidence was that the deaths occurred when she was on duty.
  • A statistician calculated the 1 in 342 million that this could be a coincidence (Elffers 2002)
  • Gill (2008) recalculated this to be between 1 in 1,000 and 1 in 25.
  • After six years in prison she was acquitted in April 2010
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21
Q

Conditional probability

A

Assumptions based on the evidence introduced during trial

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22
Q

What are the two sample types?

A
  1. Recovered or questioned samples, namely a sample of unknown origin
  2. The control or reference
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23
Q

What is the purpose of a substrate control?

A

The purpose of a substrate control can be used to distinguish between the environment and surroundings and enable us to differentiate these against the questioned samples

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24
Q

How is relative frequency calculated?

A

The relative frequency is calculated against the items observed over a period of time in a laboratory or from all the DNA profiles in some defined population

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25
Q

How should the likelihood of the evidence be calculated?

A

An expert assessment of the likelihood (or probability) of obtaining particular findings should be formed upon data relevant to the type of evidence in question. Relevant data are two different types:
1. Extensive surveys, databases or experimentation
2. Refer to the experts personal experiences and previous casework

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26
Q

The two probabilites or likelihoods

A
  1. The likelihood of the evidence if the prosecutions proposition is true”
  2. “…and the likelihood of the evidence if the defence proposition is true”
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27
Q

What does the relative value of the two likelihoods provide?

A

A measure of the meaning and the probabitve value of the evidence. Normally this is represented as the likelihood ratio.

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28
Q

What is base rate fallacy?

A

Making a probability judgement based on conditional probabilites wihtout taking into account the effect of prior probabilites.

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29
Q

What are prior odds?

A

The chance of something happening at random

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30
Q

An event which is impossible to occur would have a probability of?

A

Zero

31
Q

The probability of guilt given the evidence and vice versa is an example of what odds?

A

Posterior odds

32
Q

What fallacy caused Lucy De Berk to be falsely accussed?

A

Prosecutors fallacy

33
Q

A logical measure of chance is referrred to as what type of probability?

A

Objective

34
Q

Frequencies can be both relative and?

A

Absolute

35
Q

What is the likelihood of the evidence sometimes related to?

A

Sometimes (a) the likelihood of the evidence can be related to the (b) frequency of occurrence

36
Q

What do base rates give us a general indication of?

A

Base rates give us a general indication of the prior probability

37
Q

Basis

When probabilites are used what must be considered?

A

When probabilities are used it is vital to inspect the basis on which the subjective assessment has been made.

38
Q

Bayes theorem

A

Bayes theorem deals with the posterior probability conditioned on the prior probability and the likelihood ratio for the evidence.

39
Q

The posterior odds in favour of the prosecution proposition are equal to the product of..

A

The posterior odds in favour of the prosecution proposition are equal to the product of:
* The ratio of the probability of the evidence, if the prosecutions propositon is true
* The probability of the evidence, if the defence proposition is true (i.e. the likelihood ratio);
* The prior odds in favour of the prosecution proposition

40
Q

Reed and Reed (2009)

Low template DNA

A
  • As the science of DNA developed, techniques of analysing minute quantities of DNA (Low Template DNA) were developed from around 1999 onwards.
  • Evidence using this process was being produced since 2007
  • The case is linked to that of R v Sean Hoey and the appeals were held jointly.
  • The judge’s criticisms of LCN DNA (in Hoey) evidence in the context of a verdict which was also highly critical of many aspects of the police investigation.
  • In particular, the small number of cells (15-20) used to build a DNA profile of a suspect which also carries a greater risk of contamination
41
Q

Reed and Reed (2009)

Circumstances of the case

A
  • David Reed and Terence Reed were convicted at Teesside Crown Court in 2007 of the murder of Peter Hoe
  • Peter has been repeatedly stabbed
  • Two pieces of plastic thought to be parts of two separate knife handles were found near to Peter’s body
  • One had cellular material on it which matched the profile of David Reed and Peter Hoe and the other which matched the profile of Terence Read and another
42
Q

Reed and Reed (2009)

Match probabilites + cell site analysis

A
  • The match probabilities were such that it was accepted to be their DNA
  • One of the pieces of plastic fitted the blade of a knife which is found in a drain at Peter Hoe’s address
  • Cell site analysis put both Reed & Reed in the vicinity of Peter’s address about the time
  • Terence Reed also purchased another identical tracksuit top on the day following the killing. The prosecution contend this was because the other garment was heavily blood-stained
43
Q

Reed and Reed (2009)

Motive

A
  • David Reed, 29, was obsessed with renowned hard-man Mr Hoe and wanted to replace him as their neighbourhood’s toughest character
  • He sought several fights with the 43-year-old
  • After a drinking and drug-taking session, Reed enlisted the help of his younger brother to attack Mr Hoe
  • They struck when he returned to his home in Middlesbrough, from a visit to his mother’s house nearby Father-of-six Mr Hoe was stabbed seven times and his body was found the following day
  • Two pieces of plastic - splinters from knife handles - were discovered near the body in the front room of the terraced house
  • A blade which matched one of the handles was found in a drain at the back of the property during a police search a week later
  • Scientific tests on the fragments of plastic showed one carried David Reed’s DNA while and the other matched his brother, 26
  • The brothers were arrested after rumours spread about David’s fixation with Mr Hoe and their fights
44
Q

Stains of biological fluid are detectable by:

A
  1. Visual examination
  2. presumptive test
45
Q

What stains of biological fluid are detectable by visual examination or presumptive tests?

A
  • Blood
  • Saliva
  • Semen
46
Q

What stains of biological fluid are not detecable by visual examination or presumptive tests?

A
  1. Sweat
  2. Skin cells
  3. Vaginal secretions
47
Q

What do you need to determine the precise nature of a material?

A

It is relatively straightforward to determine the precise nature of the material if:
* It is particulate
* Or if it is a stain of biological material that can be detected by visual examination or by presumptive test

48
Q

Can you determine the precise nature of a biological material if it isnt detectable via the typical methods?

A
  • In the case, where it is not detectable by visual examination or presumptive test it is not possible to know the precise nature of the biological material from which the DNA originated
  • The material often originates from skin cells; hence the expression touch DNA
  • we may be able to attribute the profile to a particular type of bodily fluid
49
Q

How can DNA be transferred?

A
  • Primary transfer - By a person directly to the object from which the sample was taken
  • Secondary transfer - By a person to another person and by that other person to an object from which the sample was taken
  • Tertiary transfer - By a person to an object and from that object to another person and by that person to the object from which the sample was taken
50
Q

Lowe et al

A
  • The study undertaken by Lowe and others at the FSS
  • It showed that in tests and control conditions that there was a difference between individuals in their tendency to deposit or shed DNA but it was not known why.
  • Secondary transfer which results in only the cellular material of the original transfer found could occur under certain ideal conditions where clean objects and washed hands are used; the tests had shown that this happened were all the contact occurred without delay.
  • In all other cases where the delay or the different contact was either 30 minutes or an hour, a profile of the transfer raw or the intermediary was found. It would therefore be expected that unless the contacts have occurred within a very short period of time, a mix profile will be found. This paper made clear that was necessary for further work to be done
51
Q

Crime scene for 3 days

Reed and Reed (2009)

Plastic

A

Valerie Tomlinson spent three days at the crime scene
* They formed the opinion that the two pieces of plastic came from different knife handles
* Its possible the plastics relate to the weapons used in the attack
* Other than the plastic the house was clean and tidy
* The plastic fitted the blade of the knife found in the drain

52
Q

Reed and Reed (2009)

Nature of recent appeals

A

The appeals were directed at challenging the admissibility of the evidence given by Valerie Tomlinson due to:
* The manner and timing of the transfer of the apellants DNA as well as the overall reliability of LTN DNA

53
Q

Reed and Reed (2009)

Two exhibits

A
  • Plastic piece one had visible traces of blood on it since it was pert of a blood stained carpet (AC/4)
  • Plastic piece two was examined under the microscope and had no traces of blood (AC/4)
54
Q

Reed and Reed (2009)

Valerie Tomlinson intial opinion

A

Her initial opinion:
* If there were any DNA on the plastic, other than to the blood on AC/4 it was most likely to be DNA which had been transferred through touch
* It was therefore likely that the amount would be low
* And should be tested by the Low Template process which she considered reliable

55
Q

Reed and Reed (2009)

Valerie Tomlinson manner and timing of transfer

A
  • She had examined all the possible scenarios as to how the DNA of both Reed’s had been found on both pieces of plastic
  • The fact that there was no identifiable DNA profile from any other person (save Peter Hoe in the case of AC/4)
  • The DNA profiles obtained were of a quality much higher than she would ordinarily have expected from the LCN process; it was possible therefore to give some clearer guidance as to an evaluation of the possibilities of transfer
  • The fact that there were two knife handle fragments each with a profile of one of the Reed’s
  • The knives were foreign to the scene as the handles did not match any in Peter Hoe’s kitchen
56
Q

Pathologist, satisfied

Reed and Reed (2009)

DNA transfer

A
  • Valerie Tomlinson said the DNA was transferred through primary transfer
  • She was surprised that on AC/4 the DNA profile from the cells other than the blood of Peter Hoe was of the same order of contribution as the DNA profile from the blood
  • She was satisfied that the DNA could be interpreted to give a reliable profile of the other contributor of DNA on AC/4
  • She had never had results of this quality before from the LCN process. It was common for DNA transferred through touch to have results that could not be interpreted at all or showed such complex mixtures that they were difficult to interpret
  • Dr Egan (Pathologist) said the blade in the drain could have been used to inflict four of the wounds on Peter Hoe
57
Q

Reed and Reed

Apellants critisim of Valeries evidence

A
  • She had gone beyond giving admissible evidence in explaining that they had transferred their DNA by bringing the knives to the house and were handling them when they broke in.
  • Her evidence on secondary transfer was unrealistic.
  • Her conclusion that transfer must have been primary was not justified by her assertion that the profile was high-quality.
  • There was no research to sustain that opinion and it was, for that reason, inadmissible.
  • There was no way of establishing how long the cellular material had persisted.
  • She had also failed to take account that the material was found only on a fragment of each handle. She did not take into account the possibility that there might have been cellular material from others on the rest of the handle or on the blade
58
Q

Limitations of source level propositions

A
  • Do not say anything about how the evidence came to be at the scene or on the defendant’s clothing
  • Nor do they take into account such variables as the quantity, position or distribution of the recovered material
  • Source level propositions are limited to addressing whether or not a piece of evidence came from a particular source
  • Assessment of evidence under source level propositions require little in the way of circumstantial information
59
Q

Examples of source level propositions

A
  • The defendant is the source of the semen at the crime scene
  • The defendant is not the source of the semen at the crime scene
  • The defendant’s sweater is the source of the fibres at the crime scene
  • The defendant’s sweater is not the source of the fibres at the crime scene
  • The damaged window frame is the source of the paint fragments recovered from the defendant’s clothing
  • The damaged window frame is not the source of the paint fragments recovered from the defendant’s clothing
60
Q

Examples of sub-source level propositions

A
  • The DNA recovered from the crime sample came from Mr Smith
  • The DNA recovered from the crime sample did not come from Mr Smith
  • The DNA recovered from the crime sample came from some other person
61
Q

Activity level propositions

A
  • The defendant had intercourse with the victim
  • The defendant walked on the carpet in the burgled house
  • The defendant smashed the window
62
Q

Offence level propositions

A
  • The defendant raped the complainant
  • The defendant burgled the house
  • The defendant committed criminal damage
63
Q

Who decides on offence level propositions?

A
  • Offence level statements make conclusions about criminal responsibility and liability
  • This is sometimes referred to as the ultimate issue and ultimately one which the court must deal with
64
Q

Why can’t expert witnesses not testify for offence level propositions?

A

Expert witnesses should not testify to propositions at the offence level, because they involve factual and moral judgments that forensic scientists are not jurisdictionally competent to make.

65
Q

What is prior odds?

A

What’s the chance of this happening in the general population

66
Q

What does the likelihood ratio compare?

A

Two evidential propositions

67
Q

What are posterior odds?

A
  • Putting all of the data together, for the benefit of the court.
  • We multiply the prior odds and the likelihood ratio to give us the posterior or ending odds.
68
Q

What is emperical probability referred to?

A

Empirical probability is sometimes referred to as the relative frequency probability.

69
Q

Product

A

When two or more numbers are multiplied together

70
Q

Stains of biological fluid can be detected by visual examination or?

A

Presumptive tests

71
Q

The defendant walked on the carpet in the burgled house. What level of proposition is this?

A

Activity

72
Q

The defendants twitter is not the source of the fibres at the crime scene. What level of proposition does this address?

A

Source

73
Q

Where the scientist can say that the source of DNA came from a particular body fluid, what term is used here?

A

Attributable

74
Q

The non DNA evidence used in the case of Reed and Reed locating the offenders by their mobile phones?

A

Cell site analysis

Advanced Forensic Science (6 decks)

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