Psychiatric expert evidence has become increasingly important in Singapore’s criminal justice system. It helps the courts determine whether an accused person’s mental state affected their criminal responsibility, intent, or even ability to stand trial.
With growing awareness of mental health issues and their intersection with the law, psychiatric evidence has been more frequently relied upon in court. To improve consistency and ensure that such evidence is reliable and objective, the Criminal Procedure (Expert Opinion) Rules 2025 (Rules) and related legislative amendments took effect on 31 December 2025.
These new rules introduce, among other changes, a formal Panel of Psychiatrists – a register of qualified psychiatrists approved to provide expert evidence in criminal proceedings. Read on to learn more about the changes that have been brought about by the new rules, and what these entail for the use of psychiatric expert evidence in criminal trials moving forward.
What is Psychiatric Evidence?
Psychiatric evidence refers to the opinions or findings of a qualified psychiatrist about an individual’s mental condition, typically based on clinical evaluation, diagnostic tools, and recognised psychiatric criteria.
Such evidence can be presented in written reports or oral testimony, and may include assessments on:
- Whether an accused suffers from a recognised mental disorder;
- How that condition may have influenced their thoughts, intentions, or behaviour at the time of the offence (i.e. whether there was a significant contributory link between the mental disorder and the offences committed); and
- The person’s current mental state and suitability for rehabilitation or treatment.
Psychiatric evidence is distinct from ordinary witness testimony, as it draws on specialised medical knowledge to assist the court in understanding issues outside its expertise.
What is the Role of Psychiatric expert evidence in criminal cases?
Psychiatric expert evidence assists judges in making legally relevant findings about mental state and responsibility. Some common areas where it arises include:
Assessing criminal responsibility
Under section 84 of the Penal Code, a person may be acquitted of a criminal charge on the ground of unsoundness of mind if, at the time of the act, they were incapable of knowing its nature or wrongness due to a mental disorder. Psychiatric experts help the court determine whether this legal test is met. Our other article provides a detailed overview on the defence of unsoundness of mind.
The defence of diminished responsibility
The defence of diminished responsibility is a partial defence or special exception to the offence of murder under section 300 of the Penal Code in Singapore.
In such a case, psychiatric evidence may be tendered by the defence to show that the offender was suffering from a mental disorder which substantially impaired the offender’s responsibility for committing the offence. If successfully proven, this can reduce a murder charge to one of culpable homicide not amounting to murder.
Fitness to plead or stand trial
Before trial, a psychiatric evaluation may be required to determine if the accused is mentally fit to understand the legal proceedings and instruct their defence counsel.
Sentencing and rehabilitation
Even when an accused is convicted, psychiatric reports can assist in sentencing. For example, in a 2022 case, the Court of Appeal overturned a drug trafficker’s capital sentence to one of life imprisonment instead, after the court found that the offender’s major depressive disorder (MDD) and substance use disorder (SUD) had substantially impaired his mental responsibility for his acts. These disorders together had, in particular, significantly affected his ability to resist the urge to consume drugs, influencing his decision to traffic drugs as a means of feeding his drug habit. His MDD and SUD also influenced his impaired his mental responsibility for the act of trafficking itself.
Psychiatric reports can also help judges decide whether a Mandatory Treatment Order (MTO) or other rehabilitative sentences are appropriate.
In each context highlighted above, the psychiatrist acts as an expert witness, explaining the clinical findings and linking them to the relevant legal questions.
You can refer to our other article for more information on the role of expert witnesses and expert evidence in legal proceedings.
What are the Key Changes Brought About by the New Rules on Psychiatric Evidence?
The increased use of psychiatric evidence has also highlighted issues of inconsistency, bias, and quality control. Given that psychiatric findings can heavily influence verdicts and sentences, the new rules aim to:
- Strengthen the credibility of psychiatric evidence;
- Ensure expert impartiality and professional accountability; and
- Help the courts receive high-quality, consistent reports.
The key changes are:
1. Establishment of a panel of psychiatrists
From 31 December 2025, only psychiatrists listed on the Panel of Psychiatrists will be allowed to provide psychiatric expert evidence in criminal proceedings.
The Panel will be maintained jointly by the courts and the Ministry of Health (MOH). Applicants must demonstrate recognised qualifications, professional standing, and forensic experience.
A Selection Committee, typically comprising a Supreme Court judge, a District Judge, and a senior MOH official, will review applications to ensure that only competent and impartial psychiatrists are appointed. Prospective applicants must also meet the relevant eligibility criteria, including being a registered psychiatrist in Singapore, or having completed or is undergoing relevant formal training.
The Rules provide an avenue of appeal for those whose applications are rejected.
The Panel list will be publicly available, allowing lawyers and parties to engage vetted experts with confidence.
2. Duties and obligations of experts
The new Rules also codify an expert’s paramount duty to the court. This means a psychiatrist’s first obligation is to assist the judge impartially, not to advocate for the party who instructed them.
Experts must also:
- Present their opinions clearly and objectively;
- Disclose the facts, data, and reasoning behind their conclusions;
- Explain any limitations or uncertainties in their opinions; and
- Comply with prescribed standards for the format and contents of reports.
This aligns with long-standing principles in expert evidence law that emphasise independence and transparency.
3. Concurrent Expert Evidence (“Hot-Tubbing”)
To improve efficiency, courts may direct psychiatrists for both sides to testify together in a concurrent evidence session – commonly known as “hot-tubbing.”
This process allows the judge to question both experts directly, clarify areas of agreement or difference, and reach a clearer understanding, especially in cases involving complex technical issues.
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The introduction of the Panel of Psychiatrists and the Criminal Procedure (Expert Opinion) Rules 2025 represents a major milestone in Singapore’s approach to expert evidence.
By setting clearer standards for who may testify and how reports are to be prepared, the new framework enhances the objectivity, quality, and credibility of psychiatric evidence in criminal courts.
Ultimately, these reforms strengthen both public confidence and judicial integrity, ensuring that mental health assessments, while medically complex, are applied within a clear and fair legal process to ensure a just outcome for the parties in criminal proceedings.
