Criminalistiek & Bewijswaardering Samenvatting Reader (2025-2026)
Bewijs evaluatie
Association of Forensic Science Providers (2009) ‘Standards for the formulation of evaluative
forensic science expert opinion’, Science & Justice 49, 161-164.
The expert will base his opinion upon 4 principles:
1) Balance
The expert should address at least one pair of propositions based on the prosecution
issue (H0) and one on an alternative (defence issue)
2) Logic
The expert will address the probability of evidence given the proposition and NOT the
probability of the proposition given the evidence (prosecutor’s fallacy)
3) Robustness
The expert will provide an opinion that is capable of scrutiny by other experts and
cross-examination. Opinion is based on sound knowledge of the evidence types and
verified databases.
4) Transparency
The expert will be able to demonstrate how he came to his conclusion.
It is the duty of an expert to help both the prosecution, the defence, and the courts. It is
important to address the proposition at the activity level where possible. An expert will NOT
give an evaluative opinion on matters outside his area of expertise. An expert also will NOT
give an opinion on issues that don’t require expert knowledge. If asked, he must make clear
that it is NOT an expert opinion.
Guidance notes:
1) In cases where prosecutors are unable to clearly identify what happened, the expert
should operate in investigative mode to assist the police or Crown investigators and
work to identify key issue(s).
2) The expert should establish a definite scenario from the investigator, prosecution
team, defence team, or case managing judge.
3) A case where the suspects makes “no comment”, there are 3 options
I) Adopt, on behalf of defence, an alternative hypothesis
II) Explore a range of alternative explanations for the findings
III) Discuss the likelihood of the observations given the prosecutors proposition
and stress that no one can evaluate logically the weight of these observations
without an ‘alternative’
4) In cases where conditioning information may be insufficient to estimate probabilities,
the expert may operate in investigative mode to identify potential scenarios.
, If an evaluative statement is required it should be provided with a clear statement
of the assumptions made
5) Wherever possible, probability estimates should be made using published data or
unpublished data that has been peer-reviewed and documented on file
In cases where specific material or evidence type is not known to the expert,
estimates of probability should be made from technical knowledge and/or
simulated tests.
6) The opinion should express the degree of support for one proposition or the other
depending on the value of the LR
I) Values of LR close to 1: findings support each proposition equally
II) Values of LR > 1: findings provide degree of support for
prosecution’s proposition
III) Values of LR < 1: findings provide degree of support for
defence proposition
Definitions:
Evaluative opinion: An opinion of evidential weight based upon case specific propositions
and clear conditioning information (based upon the estimation of a LR).
Investigative opinion: Explanations are generated to account for observations.
Technical (factual) reporting: The ‘factual’ reporting of a test outcome based solely on the
technical competence of the individual.
Case assessment: The application of expert judgment to devise an examination strategy
based upon a framework of circumstances.
Examination strategy: A course of action based upon expert assessment that addresses the
case issue(s) to the maximum benefit to the CJS in terms of time, cost, and effectiveness.
Framework of circumstances: A summary of all the information known to the scientist about
the crime and suspect(s) that is relevant to the assessment and interpretation of the
scientific observations.
Explanation: A hypothesis (theory) that explains scientific observations. They can be
generated without mutually exclusive alternatives (unlike propositions).
Probability of an explanation: Express an opinion in the form of a probability that a
particular explanation is true.
Proposition: A formal hypothesis that is generated from the background information but
may also depend upon the observations that have been made.
- In a criminal trial: 1 represents prosecution, 1 represents defence; propositions are
mutually exclusive and exhaustive.
Evidential weight: The expression of the extent to which the observations support one of
two competing propositions. It is expressed in terms of a numerical value of the LR or a
verbal scale related to the magnitude of the LR.
, Likelihood Ratio (LR): The ratio of two probabilities. The probability of the evidence given
the prosecutor’s proposition is true divided by the probability of the evidence given the
alternative proposition is true.
- LR = P(E|H0)/P(E|H1)
Probability of a proposition: Logically incorrect to express an opinion in the form of a
probability that a particular proposition is true (prosecutor’s fallacy). Scientists should
consider the probability of the evidence given each of the propositions.
Berger, C.E.H. (2010) ‘Criminalistiek is terugredeneren, Logisch correct redeneren in
forensische rapportages ...en in de rechtszaal’, Nederlands Juristenblad, 784-789.
Kansrekening is onontbeerlijk om het redeneren in strafzaken op de meest rationele manier
uit te voeren. Lezers hebben moeite een logisch correcte conclusie zonder uitleg te
begrijpen. Hier is een schijnkeuze:
- Een logisch incorrecte conclusie die goed begrepen wordt, is GEEN alternatief voor
een logisch correcte conclusie die uitleg behoeft.
Forensische Wetenschap is de wetenschap van het terug redeneren (van een bekend gevolg
terug naar de oorzaak) met gebruik van logica, kansrekening en methodologie.
De gezamenlijke interesse van Forensisch Wetenschappers en juristen: Hoe redeneren we
van gevolg terug naar oorzaak, wanneer we met onzekerheid te maken hebben?
Er zijn 3 hoofdvormen van redeneren:
1) Abductie
Het genereren van creatieve hypothesen, die – wanneer juist – de initiële
waarnemingen het best verklaren.
2) Deductie
Type redenering waarmee je tot harde, zekere conclusies kunt komen (categorische
conclusies), die noodzakelijk juist zijn. Dit wordt toegepast wanneer een hypothese
uitgesloten kan worden (bijv. een verdachte met een waterdicht alibi).
3) Inductie
Waarnemingen die meer steun voor de ene hypothese vormen dan voor de ander,
maar geen van beide uitsluiten. Waarnemingen geven steun aan een hypothese,
maar kunnen die hypothese nooit met zekerheid bewijzen.
Twee concurrerende hypothesen moeten elkaar uitsluiten!
Onze mat van overtuiging omtrent de hypothesen kan worden uitgedrukt in een
kansverhouding (odds): Kans dat H1 waar is / Kans dat H2 waar is
Bewijs evaluatie
Association of Forensic Science Providers (2009) ‘Standards for the formulation of evaluative
forensic science expert opinion’, Science & Justice 49, 161-164.
The expert will base his opinion upon 4 principles:
1) Balance
The expert should address at least one pair of propositions based on the prosecution
issue (H0) and one on an alternative (defence issue)
2) Logic
The expert will address the probability of evidence given the proposition and NOT the
probability of the proposition given the evidence (prosecutor’s fallacy)
3) Robustness
The expert will provide an opinion that is capable of scrutiny by other experts and
cross-examination. Opinion is based on sound knowledge of the evidence types and
verified databases.
4) Transparency
The expert will be able to demonstrate how he came to his conclusion.
It is the duty of an expert to help both the prosecution, the defence, and the courts. It is
important to address the proposition at the activity level where possible. An expert will NOT
give an evaluative opinion on matters outside his area of expertise. An expert also will NOT
give an opinion on issues that don’t require expert knowledge. If asked, he must make clear
that it is NOT an expert opinion.
Guidance notes:
1) In cases where prosecutors are unable to clearly identify what happened, the expert
should operate in investigative mode to assist the police or Crown investigators and
work to identify key issue(s).
2) The expert should establish a definite scenario from the investigator, prosecution
team, defence team, or case managing judge.
3) A case where the suspects makes “no comment”, there are 3 options
I) Adopt, on behalf of defence, an alternative hypothesis
II) Explore a range of alternative explanations for the findings
III) Discuss the likelihood of the observations given the prosecutors proposition
and stress that no one can evaluate logically the weight of these observations
without an ‘alternative’
4) In cases where conditioning information may be insufficient to estimate probabilities,
the expert may operate in investigative mode to identify potential scenarios.
, If an evaluative statement is required it should be provided with a clear statement
of the assumptions made
5) Wherever possible, probability estimates should be made using published data or
unpublished data that has been peer-reviewed and documented on file
In cases where specific material or evidence type is not known to the expert,
estimates of probability should be made from technical knowledge and/or
simulated tests.
6) The opinion should express the degree of support for one proposition or the other
depending on the value of the LR
I) Values of LR close to 1: findings support each proposition equally
II) Values of LR > 1: findings provide degree of support for
prosecution’s proposition
III) Values of LR < 1: findings provide degree of support for
defence proposition
Definitions:
Evaluative opinion: An opinion of evidential weight based upon case specific propositions
and clear conditioning information (based upon the estimation of a LR).
Investigative opinion: Explanations are generated to account for observations.
Technical (factual) reporting: The ‘factual’ reporting of a test outcome based solely on the
technical competence of the individual.
Case assessment: The application of expert judgment to devise an examination strategy
based upon a framework of circumstances.
Examination strategy: A course of action based upon expert assessment that addresses the
case issue(s) to the maximum benefit to the CJS in terms of time, cost, and effectiveness.
Framework of circumstances: A summary of all the information known to the scientist about
the crime and suspect(s) that is relevant to the assessment and interpretation of the
scientific observations.
Explanation: A hypothesis (theory) that explains scientific observations. They can be
generated without mutually exclusive alternatives (unlike propositions).
Probability of an explanation: Express an opinion in the form of a probability that a
particular explanation is true.
Proposition: A formal hypothesis that is generated from the background information but
may also depend upon the observations that have been made.
- In a criminal trial: 1 represents prosecution, 1 represents defence; propositions are
mutually exclusive and exhaustive.
Evidential weight: The expression of the extent to which the observations support one of
two competing propositions. It is expressed in terms of a numerical value of the LR or a
verbal scale related to the magnitude of the LR.
, Likelihood Ratio (LR): The ratio of two probabilities. The probability of the evidence given
the prosecutor’s proposition is true divided by the probability of the evidence given the
alternative proposition is true.
- LR = P(E|H0)/P(E|H1)
Probability of a proposition: Logically incorrect to express an opinion in the form of a
probability that a particular proposition is true (prosecutor’s fallacy). Scientists should
consider the probability of the evidence given each of the propositions.
Berger, C.E.H. (2010) ‘Criminalistiek is terugredeneren, Logisch correct redeneren in
forensische rapportages ...en in de rechtszaal’, Nederlands Juristenblad, 784-789.
Kansrekening is onontbeerlijk om het redeneren in strafzaken op de meest rationele manier
uit te voeren. Lezers hebben moeite een logisch correcte conclusie zonder uitleg te
begrijpen. Hier is een schijnkeuze:
- Een logisch incorrecte conclusie die goed begrepen wordt, is GEEN alternatief voor
een logisch correcte conclusie die uitleg behoeft.
Forensische Wetenschap is de wetenschap van het terug redeneren (van een bekend gevolg
terug naar de oorzaak) met gebruik van logica, kansrekening en methodologie.
De gezamenlijke interesse van Forensisch Wetenschappers en juristen: Hoe redeneren we
van gevolg terug naar oorzaak, wanneer we met onzekerheid te maken hebben?
Er zijn 3 hoofdvormen van redeneren:
1) Abductie
Het genereren van creatieve hypothesen, die – wanneer juist – de initiële
waarnemingen het best verklaren.
2) Deductie
Type redenering waarmee je tot harde, zekere conclusies kunt komen (categorische
conclusies), die noodzakelijk juist zijn. Dit wordt toegepast wanneer een hypothese
uitgesloten kan worden (bijv. een verdachte met een waterdicht alibi).
3) Inductie
Waarnemingen die meer steun voor de ene hypothese vormen dan voor de ander,
maar geen van beide uitsluiten. Waarnemingen geven steun aan een hypothese,
maar kunnen die hypothese nooit met zekerheid bewijzen.
Twee concurrerende hypothesen moeten elkaar uitsluiten!
Onze mat van overtuiging omtrent de hypothesen kan worden uitgedrukt in een
kansverhouding (odds): Kans dat H1 waar is / Kans dat H2 waar is
