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Crime & Forensics
Evidence & Investigation
What forensic techniques can establish, and what they cannot.
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Forensic science is best defined as what?
Identification, Proof and Doubt
Most of the safeguards in a criminal trial exist because a particular kind of error kept happening. Each one has a story behind it.
About this topic
A criminal trial is not an inquiry into what happened so much as a test of whether a case has been proved to a defined standard. That framing explains a great deal of otherwise puzzling procedure: why the prosecution carries the burden, why an accused person can decline to explain themselves, why a statement made outside court is treated with suspicion when the person who made it cannot be questioned about it. The second half of the subject is empirical rather than legal. Psychologists have spent decades studying how identifications are made, how confidence in them changes after feedback, and how ordinary people can be brought to confess to things they did not do. Much of that research has fed directly back into practice, in the design of lineups and in the requirement to record interviews in full, which is one of the clearer cases of laboratory work changing what happens in a police station.
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Identification, Proof and Doubt: all 10 questions and answers
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1In a criminal trial, the burden of proof normally rests with whom?
- A The defence
- B The trial judge
- C The investigating officers
- D The prosecution Correct
Answer: D. The prosecution
Why: It follows directly from the presumption of innocence. It is also why a defendant can in principle say nothing at all and still be acquitted.
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2Beyond reasonable doubt is what?
- A A category of witness statement
- B The minimum number of witnesses required
- C The standard of proof required for a criminal conviction Correct
- D A recognised ground of appeal
Answer: C. The standard of proof required for a criminal conviction
Why: Civil cases in common-law systems use the lower balance of probabilities standard. The same events can therefore produce a civil finding and a criminal acquittal without contradiction.
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3Mens rea refers to what?
- A The caution read out on arrest
- B The mental element of an offence, such as intent or recklessness Correct
- C The physical act that makes up the offence
- D A plea based on mental illness
Answer: B. The mental element of an offence, such as intent or recklessness
Why: It pairs with actus reus, the conduct element, and prosecutors generally have to establish both. Strict liability offences are the deliberate exception that dispense with it.
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4Hearsay evidence is what?
- A A statement made outside court, offered to prove that what it asserts is true Correct
- B Rumour circulating in the press
- C Testimony given by an anonymous witness
- D Evidence given by a child
Answer: A. A statement made outside court, offered to prove that what it asserts is true
Why: The objection is that the original speaker cannot be cross-examined about it. Most systems then allow a long list of exceptions, such as dying declarations and business records.
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5Research on eyewitness identification has consistently found what?
- A Witnesses are accurate in almost every case
- B Only child witnesses make identification errors
- C Accuracy improves as the delay grows longer
- D Confidence and accuracy can come apart, particularly after a witness receives feedback Correct
Answer: D. Confidence and accuracy can come apart, particularly after a witness receives feedback
Why: Telling a witness they picked out the suspect inflates their later certainty considerably. That is why confidence is now recorded at the moment of the first identification, before anyone comments.
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6Why is a suspect shown among several similar-looking people rather than alone?
- A Because most jurisdictions require exactly eight people
- B To conceal the suspect's identity from the witness
- C So that a mistaken choice is likely to land on a known-innocent filler and expose the error Correct
- D To reduce the time an identification takes
Answer: C. So that a mistaken choice is likely to land on a known-innocent filler and expose the error
Why: The fillers act as a built-in test of the procedure itself. Warning the witness that the culprit may not be present also cuts false identifications in controlled studies.
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7A polygraph measures what?
- A Patterns of eye movement
- B Physiological signs such as breathing, pulse and skin conductance Correct
- C Electrical activity in the speech centres of the brain
- D Changes in voice pitch alone
Answer: B. Physiological signs such as breathing, pulse and skin conductance
Why: No bodily signal is unique to lying, so the instrument records arousal rather than deception. Most courts either exclude the results outright or admit them only where both sides agree.
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8False confessions are most often explained by what?
- A Prolonged pressure and suggestion, plus a belief that confessing will end the situation Correct
- B A deliberate wish to protect a friend in nearly every case
- C Simple confusion about dates and times
- D A desire for media attention
Answer: A. Prolonged pressure and suggestion, plus a belief that confessing will end the situation
Why: Recording interviews in full is the standard safeguard. It lets a court see whether a suspect knew details of the offence independently or was supplied with them.
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9Forensic genetic genealogy identifies a suspect by doing what?
- A Sequencing the genome to predict eye and hair colour
- B Comparing fingerprints across national borders
- C Testing hair samples for drug traces
- D Matching scene DNA to distant relatives in consumer ancestry databases and building out a family tree Correct
Answer: D. Matching scene DNA to distant relatives in consumer ancestry databases and building out a family tree
Why: The method reached wide attention with the Golden State Killer arrest in 2018. It has since raised persistent questions about the consent of relatives whose data ends up searched.
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10Reviews of DNA-based exonerations have most often found which factor in the original conviction?
- A Fingerprint evidence
- B Disputed financial records
- C Mistaken eyewitness identification Correct
- D Forged documents
Answer: C. Mistaken eyewitness identification
Why: Flawed forensic testimony and false confessions appear frequently too, and cases usually involve more than one factor at once. The overlap is part of why single safeguards rarely prevent a wrongful conviction on their own.
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