Topic 2 - Case, Assessment & Interpretation Flashcards
What does the Court Justice System expect of the Police & Courts?
- Intelligence – timely information to link or exclude suspect (DNA, fingerprints, mobile phones, CCTV) etc
- Corroborative evidence – to support charge/prosecution (all forensic potential discovered in casework)
- Timely scientific support through all stages of Criminal Justice System
rapid, quality, clear, good, partnership, objective
What does the Court Justice System expect of Politicians & Society?
- Rapid DNA results, quality assured casework, clear statements, good testimony
- An impact on crime, crime reduction & crime prevention
- Partnership projects in serious & volume crime
- An objective measure of ‘value’
1990
Where did CAI originate?
- Forensic Science Service became an Executive Agency of Home Office
- Direct charging of police for forensic services
- Development of forensic products (samples and other evidence)
- Costs were no longer invisible to the police
- In the early days there was a charge per item you wanted to examine
- Due to these extra costs there was a lot of attempts to cut corners and not submit certain evidential items leading to wrong conclusions
1999
Why did the CAI originate?
Experiencing a range of issues
The Forensic Science Service was experiencing a range of issues:
- Experiencing significant case backlogs & long turnaround times
- Constantly re-negotiating delivery dates
- Drowning in unnecessary examinations & lengthy (manual) analytical processes
- Struggling even to meet some court dates
- Failing to meet the needs of police & CJS clients
What year did the forensic database go live?
1995
What did the 1988 Govt Act introduce?
- There was a requirement for ‘Best Value’ although they tended to opt for the lowest cost
- Police Authorities were not exempt
- The forensic costs were no longer inivisible
- They did a cost review for better resource allocation & best value
What were the objectives of the CAI model?
CJS, relationships
- Improve decision making and resource allocation
- Improve relationships and develop partnerships
- Provide value (defined by client agency)
- Service the needs of the Criminal Justice System
What is the assessment in CAI?
How we manage, priotise and triage the demand
How many stages does the CAI model have?
3
What is the first stage of the CAI model?
- Customer requirement
- Case Information
- Customer Needs
What does the second phase of the CAI model involve?
- Case pre-assessment
- Determine forensic strategy
- Identify propositions
What does the third phase of the CAI model involve?
- Service delivery
- Forensic examination
- Evaluate outcomes
- Interpretation & Report
What should you identify first in a case?
The defence and prosecution propositions.
Determine the propositon level
Has the semen originated from the suspect?
Source level
Determine the propositon level
Has the suspect had sexual intercourse with the complainant?
Activity level
Determine the propositon level
Did the suspect rape the complainant?
Offence
What level is source level propositions?
- Level 1
- They require the least amount of information and expertise
What level is activity level propositions?
- Level 2
- Requires more expertise and information than source level but less than offence level
What level is offence level propositions?
- Level 3
- This requires the most expertise and information
Determine the propositon level
The blood on Mr C’s clothing came from Mr Z
Source level proposition
Determine the propositon level
The glass fragments came from window X
Source level
Determine the propositon level
The blood on Mr C’s clothing came from an unknown person
Source level proposition supporting the defense
Determine the propositon level
Mr A committed the burglary
Offence level
Determine the propositon level
Mr A was not present when the window was smashed
Activity level
Determine the propositon level
The DNA profile matches Mr B
Source level
Determine the propositon level
Mr C assaulted Mr X
Offence level
Determine the propositon level
The DNA profile on the swab does not match Mr A
Source level
Determine the propositon level
Mr B had sexual intercourse with Ms Y
Activity level
requirements, examination, decision, value
What does the CAI provide for investigators?
- Ensures requirements are clearly articulated
- Assists in setting forensic examination strategy
- Assists decision making
- Enhances Value (cost/time vs. usefulness = value)
Ensures a…
What does the CAI model provide for the CJS?
Discussion
- Ensures a balanced (unbiased) approach
- Ensures impartiality and transparency
- Allows discussion of strength of evidence
- Adds value (not to be confused with cost)
What is the upside down triangle for the forensic process
- Crime Scene examination (investigation)
- Laboratory examintion (evaluation)
- Court Adjudication
What is the posterior odds equation for the court?
Pr(G|E) / Pr(Ḡ|E)
What is the likelihood ratio equation for the scientist?
Pr(E|G) / Pr(E|Ḡ)
Prior odds equation
Pr(G) / Pr (Ḡ)
How can you calculate the posterior odds?
Likelihood ratio X Prior odds
What do the terms stand for in the prior odds equation?
E = evidence
G = Guilty
Ḡ = Innocent
Pr = Probability of
case, examination, propositions, reporting, theory, role
What does the CAI model provide for forensic scientists?
- Ensures clear understanding of case information and issues
- Leads to an agreed forensic examination strategy
- Defines propositions for testing
- Ensures staged examination and reporting is underpinned by sound statistical theory
- Adds value to the scientist’s role
What is the I / Information in Bayes Theorem?
Evaluation must be carried out within a framework of circumstances
What is conditioning information in Bayes Theorem?
- Conditioning information refers to the additional knowledge or data that is used to update the probability or hypothesis of an event.
- When determining the LR or other probabilities the scientist must make clear their understanding of the case circumstances relevant to their evaluation.
What must the scientist consider their observations in light of in Bayes Theorem?
The scientist must consider their observations in the light of prosecution Hp and defence Hd propositions
What must clearly be stated in Bayes Theorem?
The propositions must be clearly stated and are subject to change
What must the scientist consider in terms of probability in Bayes Theorem?
The scientist must consider the probability of their findings E if the prosecution proposition were true and if the defence proposition were true
What does the relationship of the two probabilities in Bayes Theorem determine?
The relative magnitude of these two probabilities (The Likelihood Ratio [L]) - determines the assistance provided by their findings in weighing the two propositions against each other.
What does the logic principle of Bayes Theorem require you to address?
Address the probability of the evidence E given the proposition H and the background information I
What is transposing the conditional?
The probability of the proposition given the evidence
What does the balance principle of Bayes Theorem require you to address?
Address
- Address at least one pair of propositions one based on the prosecution issue Hp and one based on an alternative or defence issue Hd
- If a reasonable alternative cannot be identified, the expert may address only the one proposition, but making it clear they cannot evaluate the strength of the evidence
What is the likelihood ratio equation?
Probability (Pr) of the Evidence (E) given The Prosecution hypothesis (Hp) and the information (I) divided by the Defence hypothesis (Hd) and the information (I)
What is a partial defence?
Where the defence will say it didn’t happen the way it was posed, they will admit to part of it but not all of it
Lab
Where are the figures for the likelihood ratio obtained?
They are a combination of the scientists experience in the case they’re working with and the lab management system
What does an LR value > 1 support?
It supports the prosecution hypothesis (Hp)
What does a LR value <1 support?
The defense hypothesis (Hd)
What does an LR value close to or equaling 1 support?
It doesn’t support the defense nor the hypothesis proposition and provides weak evidence for both
what does an LR value of 1000 support?
It provides strong evidence the supports the prosecution
What does an LR value of 0.001 support?
It provides strong evidence to support the defence.
Part 1
What are the key standards for an expert opinion?
- Establishing the key issue in the case
- Consider available, relevant information and, where necessary, request additional information
- Discuss with the relevant customer
- Identify relevant propositions
- Pre-assessment
- Identify potential outcomes
- Assign estimated probabilities
- Estimate Likelihood Ratios
- Commissions examinations to best progress the issue in the case
Part 2
What are the key standards for an expert opinion?
- Documentation (clearly on the case file)
- The key issue and propositions addressed
- Sources of data used in assigning probabilities
- Examination strategies
- Reports and statements
- Conditioning information
- Items received and examined
- Significant findings and conclusions
- Strength of evidence expressed as LR or verbal scale related to LR
- Disclosure paragraph
