Insanity Defense Law in MT
Insanity in Montana Criminal Law: What the Law Actually Says
Most people only understand the “insanity defense” from movies or true-crime TV. In popular culture, it often looks like a shortcut, someone commits a serious crime, pleads insanity, and avoids responsibility by going to a hospital instead of prison.
But in Montana, that entire concept is inaccurate.
Montana is one of only four states in the entire country that abolished the traditional insanity defense, and we did it more than forty years ago. Because of that, our criminal laws treat mental illness very differently than what most people expect.
This blog breaks down how Montana got here, what the law actually allows, what House Bill 877 clarified, and how our approach compares to national standards.
Montana Abolished the Insanity Defense in 1979
In 1979, Montana made a major decision that drastically shaped our criminal justice system:
the state abolished the traditional insanity defense.
Under Montana law today:
“Insanity” is not a defense to a crime.
That means a defendant cannot avoid guilt by arguing they were legally insane at the time of the offense. Unlike many states, Montana does not allow a verdict like:
- Not Guilty by Reason of Insanity
- Not Criminally Responsible
Those verdicts simply do not exist in Montana courtrooms.
This shift was based on a legal and philosophical idea that has guided Montana for decades:
A defendant may have a mental illness, but that does not automatically erase criminal responsibility.
What Montana Law Allows Instead
Even though insanity is not a defense, mental health is still relevant in two major ways:
1. Mental disease or defect can challenge the mental state element of a crime.
Most crimes require the State to prove a specific mental state, such as purpose, knowledge, or intent.
A defendant may present evidence of a mental disease or defect to argue:
- “I could not form the required intent,” or
- “I did not understand what I was doing in the way the statute requires.”
This does not excuse the crime outright, but it attacks whether the prosecution has met its burden of proof.
2. Mental illness can be considered at sentencing and placement.
A defendant may receive:
- a mental health evaluation
- a placement in a therapeutic environment
- supervised treatment conditions
- or a recommendation for the State Hospital
These considerations happen after guilt has been established, not instead of it.
House Bill 877: Why It Matters
House Bill 877 is part of the ongoing effort to make Montana’s approach consistent and clearly understood.
HB 877 reinforces the existing structure:
- Mental disease or defect may be used to challenge whether a defendant had the required mental state.
- Mental disease or defect may not be used as an affirmative defense to excuse criminal conduct.
- Montana continues to operate without a traditional insanity verdict.
In short, HB 877 clarified what Montana has followed since1979:
mental health matters, but it does not function as a full legal excuse.
How Montana Compares to Other States
Every state in the U.S. handles insanity differently, but Montana remains an outlier.
Here’s the correct national breakdown:
States that abolished the insanity defense (4 total)
- Kansas
- Montana
- Utah
- Idaho
These states do not allow a defendant to claim they were legally insane as a complete defense.
States using the M’Naghten Rule (approx. 25 states)
The M’Naghten Rule is the classic insanity test used for more than 100 years.
Under it, a defendant may be found insane if, because of mental disease or defect, they:
- did not understand the nature of their act, or
- did not know their act was wrong.
Most states still use some version of this rule.
States using the Model Penal Code (MPC) test (approx. 21states)
The MPC test is broader and allows a defense when a defendant, due to mental disease or defect, lacked substantial capacity either to:
- appreciate the criminality of their conduct, or
- conform their conduct to the law.
These states offer the most flexible insanity defense options.
Where Montana fits:
Montana does not use either test.
It does not offer a traditional insanity defense at all.
Why Mental Health Issues Still Matter in Montana Cases
Even though Montana abolished the insanity defense, mental health remains a critical part of many criminal cases. It affects:
- Competency to stand trial
- Ability to form the required mental state
- Treatment needs
- Sentencing decisions
- Placement in secure or therapeutic facilities
- Supervision conditions after release
Courts must still evaluate whether a defendant understands the proceedings, can assist in their own defense, and has treatable conditions that should be addressed during or after incarceration.
For many families, this process is confusing. They expect the system to work like other states, where “insanity pleas” can change the outcome of a case. But in Montana, the law places far greater weight on criminal accountability and far less on insanity-based defenses.
What Defendants and Families Should Know
If mental illness is involved in a criminal case in Montana,it is essential to understand:
- Insanity is not a legal shield.
- Mental illness can still shape the case, but only in specific, limited ways.
- Expert evaluations are often critical for challenging intent or advocating for treatment.
- Early involvement of an attorney is extremely important, especially in case involving psychosis, trauma, severe mood disorders, or competency issues.
At Ryan, Miller & Coburn, we have handled complex caseswhere mental health, criminal charges, and Montana’s strict legal frameworkintersect. Because Montana does not follow the national model, defendants andfamilies often need help understanding what the law really says and whatoptions still exist.
Conclusion
Montana’s decision in 1979 to abolish the insanity defense sets our state apart from most of the nation. While mental illness does not excuse criminal conduct here, it remains a crucial factor in determining whether the State can prove its case and how a defendant should be treatedwithin the criminal justice system.
Understanding this balance is essential for anyone facingcharges or supporting a loved one through the process.
If you have questions or need guidance, our team is here tohelp you navigate Montana’s unique criminal laws with clarity and support.
