How Massachusetts Handles Insanity Defenses in Murder Trials
At Benzaken, Maguire, Sheehan & Wood, LLP, we’ve defended clients facing the most serious charges in Massachusetts—first-degree murder, second-degree murder, and manslaughter. For individuals suffering from serious mental illness, the stakes are even higher. A murder charge can become a life-or-death legal fight where the central question isn’t who did it, but whether the defendant was legally criminally responsible at the time of the act.
This blog post explores how Massachusetts courts handle the insanity defense, particularly in homicide trials, and what every defendant, family member, or Boston criminal lawyer should understand about the process, the legal standards, and what it takes to succeed.
If you or a loved one has been charged with murder in Massachusetts, and mental illness is involved, keep reading—and reach out to our team of experienced Boston homicide defense attorneys for help.
What Is the Insanity Defense in Massachusetts?
In Massachusetts, we don’t technically use the word "insanity" in the courtroom. The legal term is lack of criminal responsibility, and it is governed by the standard set forth in Commonwealth v. McHoul, 352 Mass. 544 (1967).
Under the McHoul standard, a defendant is not criminally responsible for a crime if, at the time of the offense, they:
Suffered from a mental disease or defect, and
As a result, either:
Lacked the capacity to appreciate the wrongfulness of their conduct, or
Lacked the ability to conform their conduct to the requirements of the law.
This is sometimes referred to as a modified M’Naghten test, and it is different from federal standards or those used in other states.
Insanity vs. Diminished Capacity: What’s the Difference?
It’s important to distinguish lack of criminal responsibility (commonly called the insanity defense) from diminished capacity.
Lack of Criminal Responsibility is a complete defense. If successful, the defendant is found not guilty by reason of lack of criminal responsibility, and does not go to prison.
Diminished Capacity, on the other hand, is used to reduce the severity of the charge, such as reducing first-degree murder to manslaughter by arguing the defendant was too impaired to form the necessary intent.
Both defenses may involve mental illness, but they operate very differently in court. At Benzaken, Maguire, Sheehan & Wood, our Boston murder defense attorneys are experienced in asserting both defenses strategically—depending on what best serves our client’s interests.
Who Bears the Burden of Proof in an Insanity Defense?
Unlike most defenses, where the defendant must raise reasonable doubt, in Massachusetts, the Commonwealth has the burden of proving criminal responsibility beyond a reasonable doubt once the defense is properly raised.
In practice, this means:
If the defense offers credible evidence of mental illness, such as expert psychiatric testimony, the prosecution must prove the defendant was not legally insane at the time of the crime.
This burden applies even if the defendant admits committing the act—as long as the evidence raises a legitimate question about mental state.
This is crucial. It means the prosecution has to go beyond proving what happened—they must also prove that the defendant understood it and had control at the time.
How Is the Insanity Defense Raised in a Massachusetts Murder Case?
In a Massachusetts homicide trial, defense attorneys typically raise lack of criminal responsibility through:
Expert psychiatric testimony from a licensed forensic psychiatrist or psychologist.
Medical records, including diagnoses such as schizophrenia, schizoaffective disorder, bipolar disorder, or PTSD.
Testimony from family or witnesses about the defendant’s behavior before, during, and after the crime.
Prior hospitalizations at facilities like Bridgewater State Hospital.
Massachusetts courts allow defendants to be evaluated by court-appointed psychiatrists, including from the Department of Mental Health (DMH). The prosecution can also hire their own experts.
Often, these cases come down to a battle of the experts—which psychiatrist the jury believes more.
Bridgewater State Hospital and Forensic Commitment
If a defendant is found not guilty by reason of lack of criminal responsibility, they are not released to the public. Instead, the Commonwealth may petition to have the person civilly committed to Bridgewater State Hospital or another secure facility under G.L. c. 123, § 8(b) and § 16(b).
Commitment is based on:
A finding that the person suffers from a mental illness, and
That they are dangerous to themselves or others.
These hearings often occur immediately following the verdict. While commitment is technically civil, the process resembles a trial and can result in long-term confinement. In many cases, the defendant remains committed longer than they would have served in prison.
As experienced Boston criminal lawyers, we prepare our clients for both the trial phase and the civil commitment phase, ensuring a comprehensive defense from start to finish.
Recent Examples: Insanity Defense in Massachusetts Murder Cases
A recent high-profile trial in Plymouth County involved a young man accused of murdering both his parents. The defense raised lack of criminal responsibility due to psychosis and autism spectrum disorder. The court allowed extensive expert testimony on mental illness. The jury ultimately rejected the defense, but the case illustrated how complex—and deeply human—these trials can be.
In 2023, Essex Superior Court heard the case of a man, who shot multiple people, murdered a stranger, and raped a store clerk. the defendant admitted to the acts but claimed he lacked criminal responsibility due to severe mental illness. After hearing conflicting psychiatric testimony, the jury convicted him on all counts. Post-trial motions based on juror misconduct failed, showing how difficult it is to reverse a verdict even when mental illness is involved.
These cases show that even when the insanity defense is supported by expert evidence, juries are often skeptical—especially when the crimes are violent, random, or involve vulnerable victims.
Challenges of Winning an Insanity Defense in Massachusetts
Successfully raising a mental health defense in a murder trial is difficult. Some of the key challenges include:
1. Stigma Against Mental Illness
Jurors often believe mental illness is just an "excuse" or that defendants can "control themselves" with enough willpower.
2. Graphic Nature of the Crime
In emotionally charged cases—such as murder, rape, or crimes against children—it’s harder for jurors to accept that the defendant was “not responsible.”
3. Competing Experts
The Commonwealth almost always presents their own forensic expert who will argue the defendant was criminally responsible.
4. Conflicting Statements
If the defendant made statements to police indicating awareness of wrongdoing (e.g., attempts to hide evidence), the prosecution will use that to argue consciousness of guilt.
At Benzaken, Maguire, Sheehan & Wood, we prepare thoroughly for these challenges. We present expert testimony that is scientifically grounded, credible, and persuasive. We humanize our clients and push back against stigma. We highlight the true complexity of living with severe mental illness.
Jury Instructions and the Role of the Court
When a defendant asserts a lack of criminal responsibility, the judge gives the jury special instructions explaining the legal test and the burden of proof.
Key points in the instructions:
The Commonwealth must prove beyond a reasonable doubt that the defendant was criminally responsible.
Mental illness alone does not establish legal insanity.
The jury must decide whether the defendant could appreciate the wrongfulness of their act or conform their conduct to the law.
Judges also explain the consequences of a “not guilty by reason of lack of criminal responsibility” verdict—usually that the defendant will be committed to a secure psychiatric facility, not simply released.
Can the Defense Backfire?
Yes. In some cases, asserting an insanity defense can undermine the defense strategy if:
The jury finds the psychiatric testimony incredible or exaggerated.
The defendant’s statements or behavior suggest planning or awareness.
The defense admits too much—which can backfire if the jury rejects the mental health component.
In some cases, a better strategy may be to argue manslaughter or diminished capacity, or even to fight for outright acquittal.
Our job as your Boston homicide lawyers is to evaluate which strategy fits the facts—and how to frame it for a jury.
Frequently Asked Questions: Insanity Defense in MA Murder Trials
Can anyone claim insanity?
No. The defense must be supported by credible evidence—usually through psychiatric evaluation and expert testimony.
Will I go free if I’m found not guilty by reason of lack of criminal responsibility?
Not immediately. You may be civilly committed to Bridgewater or another secure hospital if deemed mentally ill and dangerous. Very often this means a life sentence in a hospital.
How do juries react to the insanity defense?
Often with skepticism. That’s why presentation, expert credibility, and jury selection are critical.