Medical And Psychiatric Evidence In Trials
1. Overview of Medical and Psychiatric Evidence in Criminal Trials
Medical and psychiatric evidence plays a crucial role in criminal trials, particularly in:
Establishing cause of death (forensic pathology)
Assessing injuries (assault, domestic violence)
Determining mental state (insanity, fitness to stand trial)
Evaluating diminished responsibility or automatism
Supporting sentencing decisions (mitigation)
Key Sources of Evidence
Medical Evidence
Autopsy reports
Toxicology reports
Clinical examinations
Expert testimony on injuries or disease
Psychiatric Evidence
Mental disorder assessments
Risk of reoffending
Capacity to appreciate the nature of the act
Fitness to stand trial
2. Admissibility of Medical and Psychiatric Evidence
Courts in Canada assess admissibility using principles derived from the Common Law and the Criminal Code, notably:
Relevance
Evidence must be directly relevant to an issue in the trial (e.g., intent, mental state).
Competence of the Expert
Witness must be qualified in medicine or psychiatry.
Reliability
Methods used must be scientifically accepted (R v. Mohan [1994] 2 S.C.R. 9).
Avoiding Prejudice
Evidence must not unduly bias the jury (s. 11(d), s. 7 Charter considerations).
Fitness to Stand Trial
Mental capacity to understand proceedings and instruct counsel (s. 2 of Criminal Code, s. 7 Charter).
Insanity Defence (s. 16 Criminal Code)
Accused must prove that at the time of the offence they suffered from a mental disorder making them incapable of appreciating the nature or wrongfulness of the act.
3. Important Case Law
Case 1: R v. Mohan [1994] 2 S.C.R. 9
Facts: The accused wanted to introduce expert psychiatric evidence to support diminished responsibility.
Issue: Is expert evidence admissible?
Decision: Supreme Court established four criteria for admissibility:
Relevance
Necessity in assisting the trier of fact
Absence of exclusionary rules
Properly qualified expert
Significance: Mohan test is the benchmark for admitting medical and psychiatric evidence in Canada.
Case 2: R v. Swain [1991] 1 S.C.R. 933
Facts: Swain was found not guilty by reason of insanity. He challenged indefinite detention in psychiatric facility.
Issue: Constitutionality of detaining accused indefinitely without review.
Decision: Supreme Court ruled that accused must be reviewed periodically, balancing public safety and individual rights (s. 7 and s. 9 Charter).
Significance: Sets standards for psychiatric evidence and post-acquittal detention.
Case 3: R v. Chaulk [1990] 3 S.C.R. 1303
Facts: Chaulk claimed insanity due to mental disorder at the time of the offence.
Issue: Standard of proof for insanity.
Decision: Court ruled that accused bears the burden of proving insanity on a balance of probabilities, using psychiatric evidence.
Significance: Confirms role of psychiatric assessments in establishing mental disorder defences.
Case 4: R v. J.-L.J. [2000] 2 S.C.R. 600
Facts: Psychiatric evidence was used to determine whether the accused had the capacity to testify.
Issue: Admissibility and weight of expert evidence on competence.
Decision: Court emphasized that experts can assist but ultimate decision rests with judge.
Significance: Establishes limits on psychiatric evidence, ensuring it aids rather than usurps judicial functions.
Case 5: R v. Stone [1999] 2 S.C.R. 290
Facts: Stone claimed “automatism” (temporary mental incapacity) causing involuntary action in a violent assault.
Issue: Can psychiatric evidence support automatism or self-induced mental disorders?
Decision: Supreme Court allowed expert testimony but emphasized distinguishing between sane and insane automatism, affecting verdict and sentencing.
Significance: Psychiatric evidence critical in automatism and criminal responsibility.
Case 6: R v. S.(R.D.) [1997] 3 S.C.R. 484
Facts: Accused argued diminished capacity due to mental disorder in sexual assault case.
Issue: Reliability of psychiatric evidence and its impact on mens rea.
Decision: Court allowed evidence but clarified that mental disorder must directly affect criminal intent.
Significance: Psychiatric evidence must link directly to the criminal act or mens rea to be probative.
4. Key Principles from Case Law
Admissibility Criteria: Mohan test (R v. Mohan) – relevance, necessity, competence, reliability.
Insanity Defence: Accused must prove mental disorder affecting ability to understand act or wrongfulness (R v. Chaulk, R v. Swain).
Fitness to Stand Trial: Periodic assessments and reviews necessary (R v. Swain).
Automatism/Diminished Capacity: Psychiatric evidence can support involuntary action or mens rea reduction (R v. Stone, R v. S.(R.D.)).
Limits of Expert Testimony: Experts assist the court but do not replace judicial fact-finding (R v. J.-L.J.).
5. Summary Table
| Case | Issue | Type of Evidence | Key Principle |
|---|---|---|---|
| R v. Mohan (1994) | Admissibility of expert evidence | Psychiatric | Mohan test – relevance, necessity, competence, reliability |
| R v. Swain (1991) | Detention post-acquittal by insanity | Psychiatric | Periodic review of mental health detention; Charter rights |
| R v. Chaulk (1990) | Standard of proof for insanity | Psychiatric | Burden of proof on balance of probabilities |
| R v. Stone (1999) | Automatism defence | Psychiatric | Differentiate sane vs insane automatism; supports involuntary action |
| R v. J.-L.J. (2000) | Competence to testify | Psychiatric | Expert assists but does not replace judicial decision |
| R v. S.(R.D.) (1997) | Diminished capacity/mens rea | Psychiatric | Evidence must show direct link to criminal intent |
Medical and psychiatric evidence is central to assessing criminal responsibility, intent, and fitness. Canadian courts ensure that it is rigorously scrutinized for reliability, relevance, and proper use, balancing individual rights with public safety.
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