Mental Illness in Criminal Justice: Understanding and Addressing the Challenges

Mental illness is one of the most misunderstood factors in the criminal justice system. When someone with a psychiatric disorder comes into contact with the law, it raises difficult questions – about responsibility, fairness, and what justice actually looks like. The intersection of mental health and criminal behaviour is not just a legal issue; it’s a deeply human one. And getting it right matters, because the stakes involve both public safety and the well-being of some of society’s most vulnerable individuals.

What is mental illness in a forensic context? 🔗

Mental illness refers to a broad range of conditions that significantly affect a person’s thinking, emotions, or behaviour. These include disorders like schizophrenia, bipolar disorder, major depressive disorder, post-traumatic stress disorder, and various personality disorders. In everyday life, these conditions can impair a person’s ability to function at work, maintain relationships, or care for themselves. In a forensic setting – where psychology meets the legal system – mental illness takes on additional significance because it can affect how a person is treated by courts, prisons, and the justice system as a whole.

It’s critical to understand that having a mental illness does not make someone a criminal. Research consistently shows that the vast majority of people living with mental health conditions are not violent and are, in fact, more likely to be victims of crime than perpetrators. The Treatment Advocacy Center has noted that individuals diagnosed with severe conditions like schizophrenia are more likely to be crime victims than offenders. This distinction is essential in any discussion about mental illness and criminal justice.

The scale of mental illness in the criminal justice system 🔗

Despite the fact that mental illness doesn’t cause crime, people with psychiatric disorders are vastly overrepresented in jails and prisons. According to SAMHSA (Substance Abuse and Mental Health Services Administration), roughly 44% of people in jails and 37% of those in prisons have a mental illness – compared to about 18% in the general population. These numbers tell a stark story about systemic failures in community mental health care.

A large-scale systematic review published in The Lancet Public Health in 2025 examined data from 43 countries and found that the prevalence of depression among incarcerated people was approximately 12.8%, while the prevalence of psychotic disorders was about 4.1%. These rates are significantly higher than what is found in the general community. The review also found that people in prisons in low- and middle-income countries had even higher rates of depression compared to those in high-income nations.

The Bureau of Justice Statistics reported that about 43% of state prisoners and 23% of federal prisoners had a history of a mental health problem. Female inmates reported even higher rates of serious psychological distress than their male counterparts.

This overrepresentation is often attributed to a phenomenon known as the criminalization of mental illness. As community-based mental health services have been underfunded or dismantled over the decades – a legacy of deinstitutionalization – many individuals with untreated psychiatric conditions end up cycling through the criminal justice system rather than receiving appropriate care.

Mental illness and criminal behaviour: what’s the actual link? 🔗

The relationship between mental illness and criminal behaviour is complex and frequently overstated in popular media. While certain untreated conditions – particularly those involving psychosis or severe mood instability – can increase the risk of erratic or aggressive behaviour, this accounts for only a small portion of all crime. Factors such as substance abuse, poverty, homelessness, and lack of social support play a far greater role.

Co-occurring disorders – where a person has both a mental illness and a substance use disorder – create especially high risk. Individuals with these dual diagnoses are more likely to experience homelessness, unemployment, and repeated contact with the justice system. The presence of co-occurring conditions can also complicate forensic assessments, making it harder to determine a person’s mental state at the time of an offence or their fitness for trial.

The “revolving door” phenomenon 🔗

One of the most troubling patterns in forensic mental health is what experts call the revolving door – people with mental illness cycling repeatedly between hospitals, jails, and the streets. As noted in research published in the World Psychiatry journal, deinstitutionalization has contributed to this pattern, with many chronically ill individuals ending up homeless or incarcerated because community supports are inadequate. Some forensic psychiatrists describe a “double revolving door” where patients circulate between mental health institutions and the correctional system without receiving sustained treatment in either setting.

Fitness to stand trial (competency to stand trial) 🔗

One of the most important legal questions involving mentally ill defendants is whether they are competent to stand trial – sometimes called “fitness to stand trial.” This concept is rooted in the principle of due process: a person cannot be tried for a crime unless they can meaningfully participate in their own defence.

The landmark U.S. Supreme Court case Dusky v. United States (1960) established the standard that is still used in most jurisdictions. Under this standard, a defendant must have a rational and factual understanding of the proceedings and be able to consult with their attorney with a reasonable degree of rational understanding.

How competency is assessed 🔗

When a question arises about a defendant’s mental fitness, a judge can order a competency evaluation. This is conducted by a forensic psychologist or psychiatrist who interviews the defendant, reviews their psychiatric history, and administers psychological tests. The evaluation focuses on the defendant’s present mental state – not their state at the time of the offence.

Key areas assessed include whether the defendant understands the charges against them, can identify the roles of courtroom participants (judge, prosecutor, defence attorney), and can make rational decisions about legal strategy. If a defendant is found incompetent, the criminal proceedings are paused. The defendant is typically sent to a treatment facility – often a state psychiatric hospital – for competency restoration, which usually involves medication and therapy aimed at stabilising their condition enough to proceed with trial.

It’s worth noting that competency is not a permanent status. A person’s mental state can fluctuate, and they may be re-evaluated multiple times throughout the legal process. Someone can be found competent at one point and incompetent at another, depending on the course of their illness or their response to treatment.

The insanity defence 🔗

While competency deals with a defendant’s current mental state during legal proceedings, the insanity defence looks backward – it asks whether the defendant’s mental illness affected their state of mind at the time of the crime. A defendant who successfully raises this defence is found “not guilty by reason of insanity” (NGRI), meaning they committed the act but lacked the mental capacity to be held criminally responsible.

Key legal tests for insanity 🔗

Several legal standards have been developed over time to define insanity, and different jurisdictions use different tests:

The M’Naghten Rule (1843): This is the oldest and most widely used test. It originated from a British case where Daniel M’Naghten killed the secretary of the Prime Minister under the delusion that the Prime Minister was conspiring against him. Under this test, a defendant is considered insane if, due to a mental disease, they did not understand the nature of their actions or did not know that what they were doing was wrong. This test is still used in nearly half of U.S. states.

The Irresistible Impulse Test: This test supplements the M’Naghten Rule by addressing situations where a defendant knew their actions were wrong but was unable to control their behaviour due to a mental illness. It focuses on the volitional aspect – could the person stop themselves from acting? – rather than purely on cognitive understanding.

The Model Penal Code Test (ALI Standard): Developed by the American Law Institute in 1972, this test states that a person is not responsible if, due to a mental disease or defect, they lacked substantial capacity to either appreciate the wrongfulness of their conduct or to conform their behaviour to the law. It was designed as a more flexible standard that accounts for the nuanced realities of mental illness.

The Insanity Defense Reform Act (1984): After John Hinckley Jr. was acquitted by reason of insanity for his assassination attempt on President Reagan, Congress passed this act for federal cases. It shifted the burden of proof from the prosecution to the defence and raised the evidentiary standard, requiring defendants to prove insanity by clear and convincing evidence.

Common misconceptions about the insanity defence 🔗

The insanity defence is far rarer than most people believe. Studies suggest it is raised in less than 1% of criminal cases and is successful even less often. When it does succeed, defendants are not simply released – they are typically committed to a psychiatric institution, sometimes for longer than they would have served in prison. Public perception, heavily shaped by high-profile cases and media portrayals, often overestimates both the frequency and the leniency of this defence.

It’s also important to know that some U.S. states – including Idaho, Kansas, Montana, and Utah – have effectively abolished the traditional insanity defence, though mentally ill defendants in these states can still be found unfit to stand trial.

The role of forensic psychological assessments 🔗

Forensic psychologists and psychiatrists play a central role in how the criminal justice system handles mentally ill individuals. Their evaluations inform some of the most consequential decisions in a criminal case – from whether someone can stand trial to whether they should be sentenced to prison or diverted to treatment.

Types of forensic assessments 🔗

Beyond competency and insanity evaluations, forensic mental health professionals conduct several other types of assessments. Risk assessments evaluate the likelihood that an individual will engage in violent or criminal behaviour in the future. These are used in sentencing decisions, parole hearings, and civil commitment proceedings. Sentencing evaluations provide courts with psychological context that may serve as mitigating factors, helping judges make more informed decisions. Malingering assessments are designed to determine whether someone is faking or exaggerating mental health symptoms for legal advantage – a critical concern in forensic settings.

Recent research from Norway, as noted in the forensic psychology literature, shows a growing trend toward using structured assessment tools in criminal responsibility evaluations. These standardised instruments help improve consistency and reduce subjectivity in forensic decision-making.

Challenges and the path forward 🔗

The criminal justice system was not designed to be a mental health system – yet that is precisely what it has become for many people. Correctional facilities often lack the resources, training, and infrastructure to provide adequate psychiatric care. Incarceration can worsen mental health symptoms, and people with untreated conditions are at higher risk for solitary confinement, disciplinary issues, and longer sentences.

Diversion and reform efforts 🔗

To address these challenges, many jurisdictions have adopted diversion programs that aim to redirect people with mental illness away from the criminal justice system and toward community-based treatment. SAMHSA’s Sequential Intercept Model identifies multiple points in the justice process where intervention can occur – from pre-arrest crisis response to post-incarceration re-entry support.

Mental health courts are another reform that has gained traction. These specialised courts work with forensic mental health professionals to create treatment-focused plans rather than purely punitive responses. Participants may receive supervised treatment in the community instead of jail time, with regular check-ins and accountability measures.

Crisis Intervention Teams (CIT), which train law enforcement officers to recognise and respond to mental health crises, have also shown promise in reducing unnecessary arrests and use of force during encounters with people experiencing psychiatric emergencies.

Why specialised assessment matters 🔗

Ultimately, the quality of justice for mentally ill offenders depends on the quality of the assessments used to understand their conditions. Poorly conducted evaluations can lead to wrongful convictions, inappropriate sentencing, or the release of individuals who still pose a risk. Forensic mental health professionals must balance their clinical expertise with an understanding of legal standards – a uniquely challenging dual role that requires rigorous training and ongoing education.

What do you think? Should the criminal justice system invest more in diversion and treatment programs for mentally ill offenders, or is the current balance between accountability and mental health support adequate? How do you think public misconceptions about mental illness and violence affect the way these cases are handled in court?

References

1. https://www.samhsa.gov/mental-health/what-is-mental-health/conditions/schizophrenia
2. https://www.tac.org/reports_publications/serious-mental-illness-prevalence-in-jails-and-prisons/
3. https://www.samhsa.gov/communities/criminal-juvenile-justice/about
4. https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(24)00280-9/fulltext
5. https://bjs.ojp.gov/library/publications/indicators-mental-health-problems-reported-prisoners-survey-prison-inmates
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC1525122/
7. https://www.law.cornell.edu/wex/insanity_defense
8. https://en.wikipedia.org/wiki/Forensic_psychology