Case Assessment and Interpretation Flashcards
what is expected from forensic scientists from the court and police (2)
intelligence on topics people do not know about
providing evidence and timely scientific support
what is expected of forensic scientists from the politicians and rest of society (3)
rapid results which are not always achievable
an objective opinion
crime reduction and prevention
what is CAI
a logical detailed assessment of what you are doing before you open the evidence bag
consider what you have been asked to do and what is needed for the case
not done in all countries but done in UK
why was CAI brought about
in the 1998
the forensic science service had a large backlog and long turnaround times
drowning in unnecessary analysis times and struggling to meet deadlines
failing to meet needs of court and police
what is the purpose of CAI (7)
- improve the use of resources
- improve decision making process
- prevent wasting time
- service the needs of the justice system
- need for the people asking to be more specific (eliminate term forensicate)
- improve relationships between police and scientists
- give value
why is preventing wasting time important
for case turnaround as the demand can be high for scientists
things that take longer = higher cost
what could be correlated to people not submitting evidence because of the cost that comes with it
miscarriages of justice
what two things must be set in CAI
your propositions
prosecution and defence ones
when is a proxy proposition necessary
what is this also called
when the offender gives a no comment so we are unaware of the defence being put forward
could also be called the alternative proposition - in the absence of this it is impossible to evaluate your findings
give two common defence strategies
self defence
contamination during evidence collection or analysis
is case context necessary in CAI
yes, in order to set your propositions and set your examination strategy by considering what is needed for the case
be careful of bias though - even if it is subconscious
what is the forensic strategy
what 7 things does it involve
a systematic approach to gathering and analysing evidence to make interpretations that can be presented in court
involves:
evidence identification
preservation
examination + analysis
documentation
interpretation
reporting
expert testimony
what does CAI enhance in the evidence you present
THE VALUE OF IT
value is not the lowest cost
what document provides information of CAI for experts in forensic science
the best practice manual for crime scene investigation from ENFSI
give two things to be considered when you are setting you examination strategy
probative value of methods
destructive techniques
what is there a need for in your CAI
good communication of the expected outcomes
what are the two elements of CAI
assessment = how you are going to manage your evidence, what analyses you are going to prioritise
interpretation = how are you going to report the findings in a logical, quantitative and accessible way to aid the understanding of what you have done to others
what are the three stages in CAI
- customer requirement, need and case info
- pre-assessment, determine forensic strategy and make propositions
- examination, evaluate outcome, interpret and report
what should you do if a customer directs you to an examination strategy you feel is inappropriate
advise them why and suggest how else it should be done with their aims still present
discuss the limitations with them
what are the aims and benefits of case pre assessment (5)
- can consider potential findings beforehand
- set out most appropriate examination strategy
- find hypotheses
- set the findings you will prioritise
- assign probabilities to the LR and then these can be refined when the evidence has been analysed
what statement is good to include at the beginning of your report
if further evidence or info comes to light it may be necessary for me to reconsider my conclusions
in the assessment of evidence, what are the hierarchy of propositions
sub source
source
activity
offence
give an example of a sub source proposition
two DNA profiles matching
give an example of a source proposition
the blood on X’s clothing came from Y
the glass fragment came from window X
give an example of an activity proposition
Mr A was present when the window was smashed
Mr has sexual intercourse with Mrs
give an example of an offence proposition
Mr A committed the burglary
Mr assaulted Mr
what type of propositions can expert witnesses generally only give
source or sub source
how much evidence does an activity level proposition generally need
more than 1
why cant we give activity level propositions
due to evidence transfer
and we weren’t actually there so it would be hearsay
who determines offence level propositions
the court/jury
give 5 things CAI requires to be effective
- good communication between parties
- an understanding of the requirements
- agreement on a forensic strategy
- understand the expected outcomes
- explore the staged approach when needed
what are the three stages in the forensic process
investigation
evaluation
adjudication (court)
does everything from crime scene examination reach the court
no it is not always needed
what is the staged approach in forensic science
what three things does this ensure
a part of CAI = a systematic process used by investigators to examine and analyse evidence
used as a flow chart
ensures the thoroughness, accuracy and reliability
what are the 8 stages in the staged approach
- incident or arrest
- recognition - identify potential evidence
- documentation - contemporaneous notes, sketch, photos
- collection - use of tools and techniques avoiding evidence contamination and damage
- preservation - package, label, store
- analysis - scientific methods
- interpretation - draw conclusions based on scientific findings
- reconstruction - of events based on evidence
how does the staged approach help forensic scientists (7)
- ensure we have clear understanding of case and issues
- defines propositions for testing
- adds value to scientists role
- agreed forensic strategy
- prevents time and money wasting
- prevents overloading of samples
- ensure everyone is doing the same process
what is Bayesian reasoning in forensic science
applying Bayesian probability theory to evaluate and interpret forensic evidence within the context of a criminal investigation for legal purposes
what are the key elements involved in Bayesian Reasoning in forensic science
(5)
- prior odds
- likelihood ratio
- Bayes theorem
- posterior odds
- making informed decisions
what does Bayesian reasoning help us do in forensic science (3)
quantify and integrate the strength of evidence into the overall case
assessing the significance of our findings by enhancing objectivity and reliability of expert testimony in court
make informed decisions
what is bayes theorem
a statistical principle used to assess the probability of a hypothesis
quantifying how strongly evidence supports or rejects a hypothesis
what are the two categories in Bayes Theorem
logic = addressing probability of evidence given the hypothesis and the background information
balance = address the two propositions and if only one can be addresses state why and give a proxy proposition
what must be stated about the propositions you put forward
they are subject to change based on new info or when you actually start analysing the evidence
what are the 4 pieces that make up bayes theorem
combined what do these provide
I = case/background information
E = scientific evidence
Hp = prosecution hypothesis
Hd = defence hypothesis or alternative proposition
the likelihood ratio
What is the likelihood ratio and what is it used for
a statistical measure of quantifying the strength of evidence
weighs the two propositions against each other and see which is supported more strongly
the probability of the evidence given the prosecution hypothesis and information divided by the defence hypothesis and information
what kind of probabilities does the likelihood ratio use
conditional probabilities
what are the prior odds
the odds of a hypothesis before any new evidence has been taken into account
your initial belief on the likelihood of the hypothesis being true or false
what are the posterior odds
the updated odds of the hypothesis after the evidence has been examined
calculated by doing prior odds x likelihood ratio
what happens if only one proposition can be given by the scientist
it is fine for the expert can only address one proposition but this should be made clear and the fact they cannot evaluate the strength of the evidence
what is transposing the conditional
should it be done
what is this a synonym for
give an example of a case where this was seen
the probability of the proposition (the accused being guilty) given the evidence
no
the prosecutors fallacy
R vs Doheny
give an example of a statement that represents transposing the conditional
normal = assuming our subject is a basketball player would be fair to conclude he is tall
transposing the conditional = assuming they are tall assumes they are a basket ball player
what happened in the R vs Doheny Case
considering DNA profile matches
expert witness was misled to answering a question and he gave his opinion that the accused left the stain at the scene
he transposed the conditional due to the questions he was being asked on the stand
what is the base rate and how is this calculated
this is the prior odds of an event occurring in the absence of background info or evidence
represents the general occurrence of something in everyday life of a given population
calculated = the probability of the event e.g the probability of a certain crime happening the a city
BASED ON CONDITIONAL PROBABILITIES
what does a likelihood ratio of more than 1 support
supports prosecution hypothesis
what does a likelihood ratio of 0 support
neutral - supports neither hypothesis
what does a likelihood ratio of less than 1 support
supports defence hypothesis
how do we get the values used in calculating likelihood ratios
use estimated values based on past cases from the experts professional experience or using databases e.g the laboratory management system
what likelihood ratio value extremely strongly supports the hypothesis
more than 1 million
what likelihood ratio value very strongly supports the hypothesis
10,000 - 1 million
what likelihood ratio value strongly supports the hypothesis
1,000 - 10,000
what likelihood ratio value moderately strongly supports the hypothesis
100 - 1,000
what likelihood ratio value moderately supports the hypothesis
10 - 100
what likelihood ratio value weakly supports the hypothesis
1 - 10
what is there no need to examine all evidence that has been submitted (3)
reduce cost and turnaround time
too much info can confuse people
take the staged approach and only use what is needed
what are potential evidence types you many come across in the assessment part of CAI
how will these affect the order you analyse things
blood
urine
DNA
fibres
hairs
paints
think what is likely to persist longer and examine that last
what two things do you need to consider when deciding the order of analysing different evidence types
transfer and persistance
transfers can be direct or indirect
what things affect the transfer of evidence (7)
pressure
number of contacts
how easily it transfers
liquid or solid
how much is involved in the contact
substrates transferred to and from
weather conditions - how evidence will persist (degradation)
what are the expectations of the expert in the interpretation of evidence they have analysed (8)
explain to the non expert
clear and concise
good communication
good scientific methods
don’t use misleading statements like might have or could have
explore all reasons for the outcomes you found
use of propositions and likelihood ratio
clear methods and examination strategy
what is an example of a case that shows as an expert you need to consider other possible reasons for the outcomes you found
the Birmingham Six
