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The National Trial Lawyers
Greater Lowell Bar Association

Mental Health Defenses

In order for a defendant to be convicted of a crime, the Commonwealth has to establish he was criminally responsible (sane) at the time he committed the crime and is competent during the trial. While they both constitute mental health defenses, criminal responsibility and competency are distinct legal principles. An attorney who represents a mentally ill criminal defendant ought to consider whether his client lacked criminal responsibility, is incompetent, or both. Procedurally the defense attorney usually raises the issue first and the defendant is then examined by a mental health expert. The parties will then litigate whether the defendant has a valid mental health defense.


Criminal responsibility examines a defendant’s state of mind at the time he allegedly committed the crime. If the defendant was either: (1) unable to appreciate the wrongfulness of his actions; or (2) understood his actions were wrong but was unable, due to mental illness or defect, to conform his behavior to the law, he was not criminally responsible for his actions. Lack of criminal responsibility is commonly known as not guilty by reason of insanity. Unlike competence, criminal responsibility cannot change with the passage of time because it is a snapshot of the defendant’s mental state at the time the crime was committed.

Cases involving this defense often devolve into a battle of experts. The defendant will generally call an expert to testify he was not criminally responsible for his crime. The Commonwealth will often call its own expert to rebut the defense expert’s opinion.

Lack of criminal responsibility defenses are notoriously hard to win. Juries are extremely reluctant to acquit defendants who admit to criminal behavior, regardless of whether they were sane or not at the time of the crime. In Massachusetts (as in most, if not all, other jurisdictions), a defendant who is found not criminally responsible of committing a serious crime is not ordinarily released from custody. Instead, the prosecutor usually asks the judge to order the defendant to be committed to a locked mental health facility to receive treatment for his mental illness. The defendant will not be released back into society until a judge concludes he no longer poses a danger.


Competency is a legal principle that addresses a defendant’s current mental state. Before any criminal case can proceed to trial, a defendant must be competent. Competence means the defendant must be able to: (1) presently consult with his attorney with a reasonable degree of rational understanding; and (2) understand the nature of the proceedings against him. Competency is fluid – a defendant can be competent one day and incompetent the next. Competency can change based on a number of factors, including medication, counseling, or a fundamental change in the defendant’s mental health diagnosis.

If a defendant is found to be incompetent to stand trial, his case is not automatically dismissed. Instead, the case remains open and is continued with the hope that the defendant will eventually become competent. If the defendant does become competent, the case against him will proceed in the normal course. While the case is being continued, the defendant might be released on bail or he might be committed to a mental health facility.

If the defendant never becomes competent, his criminal case will be dismissed once it has been open for half of the maximum time period he could have been sentenced to jail. For example, if a defendant is charged with a crime that carries a maximum sentence of 10 years in prison, and he is incompetent for five years while the case is pending, the charge will be dismissed at the five-year mark. However, judges have discretion to dismiss criminal cases earlier if they find doing so would be in the interest of justice.

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