Diminished capacity; People v Carpenter; Legal insanity; MCL 768.21a; Guilty but mentally ill (GBMI); MCL 768.36; Specific intent; Mens rea; Mental illness; Intellectual disability; Evidentiary rules; MRE 401; MRE 403; MRE 702; Notice of expert defense; MCL 767.94a; MCR 6.201(B); Stare decisis; Retroactivity; People v Robinson

The court held that MCL 768.21a does not bar a defendant from presenting diminished-capacity evidence to contest the specific-intent element of a charged offense and overruled Carpenter. Defendant, charged with open murder, AWIM, and felony-firearm for allegedly shooting two companions, sought to present expert evidence that mental illness and intellectual disability negated specific intent. The trial court denied the motion under Carpenter. On appeal, the court held that Carpenter was wrongly decided because it treated the legal-insanity statute as foreclosing evidence that does not assert insanity but instead challenges mens rea. The court reasoned that the statute “on its face addresses only the affirmative defense available to a legally insane defendant,” and “simply does not state or imply anything about the availability of diminished-capacity evidence to negate a specific element of a crime.” It emphasized that insanity is an affirmative defense that “admits guilt but seeks to excuse it,” while diminished-capacity evidence “challenges the prosecution’s case” by disputing whether defendant had the required mens rea. The court also held that the GBMI statute did not support Carpenter because it applies “only to a defendant asserting an insanity defense,” and allowing diminished-capacity evidence does not render the statutory scheme superfluous. Turning to stare decisis, the court held that Carpenter should be overruled because its flawed statutory analysis displaced a common-law defense without clear legislative abrogation. It reasoned that reliance interests did not justify retaining Carpenter because prosecutors still must prove every element beyond a reasonable doubt, evidentiary rules will govern admissibility, and defendants have long argued that Carpenter impeded their ability to present a defense. The court acknowledged operational burdens but concluded that convenience is “a poor reason to continue to prohibit” a defense rooted in common law. Finally, the court found that Carpenter’s all-or-nothing rule was increasingly out of step with modern understanding of mental illness and intellectual disability, and that successful use of diminished capacity will not free defendants from liability because the state may still prove a general-intent offense. Vacated and remanded.

Chief Justice Cavanagh concurred, joined by Justice Welch. She emphasized that today’s decision “should not be interpreted as a free-for-all” for mental-illness or intellectual-disability evidence. Trial courts must still apply MRE 401, 403, and 702, and expert-defense notice requirements remain relevant under MCL 767.94a and the newly adopted MCR 6.201(B).

Justice Welch also concurred. She wrote separately to highlight retroactivity principles, noting that today’s decision will likely prompt postconviction motions. She emphasized that courts should look to Robinson and related cases, and that Michigan’s retroactivity framework permits courts to consider “the practical challenges placed upon the criminal justice system.”

Justice Hood also concurred. He agreed Carpenter was wrongly decided and should be overruled, but wrote separately to identify “logistical, operational, and funding challenges” the decision will create. He was especially concerned that diminished-capacity evaluations could strain existing mental-health infrastructure, slow criminal cases, affect speedy-trial interests, and generate “a wave of postconviction motions and appeals.”

Justice Zahra dissented. He would have retained Carpenter, reasoning that it correctly interpreted MCL 768.21a as part of a statutory scheme governing mental illness and criminal responsibility. He argued the majority’s diminished-capacity rule undermines legislative choices, creates “new and thorny questions,” and disregards stare decisis where Carpenter had been applied for nearly 25 years.