Post‑Crime Psychiatric Diagnosis Is Relevant to Penal Law § 40.15 and Cannot Be Precluded as “Speculative” When Grounded in Pre‑Incident Records

1. Introduction

In People v Williams, 2026 NY Slip Op 04095 (App Div, 4th Dept June 26, 2026), the Fourth Department reversed a Monroe County judgment of conviction and ordered a new trial after concluding that the trial court improperly precluded a defense psychiatrist from testifying in support of the affirmative defense of lack of criminal responsibility by reason of mental disease or defect (Penal Law § 40.15).

The case arose from an incident in which the defendant’s grandmother called 911 seeking assistance due to the defendant’s abnormal behavior and mental health concerns. After an officer coaxed the defendant out from under a bed, the defendant attacked without warning, repeatedly punching and stabbing the officer, inflicting severe injuries including permanent loss of vision. A jury convicted the defendant of attempted aggravated murder, attempted murder in the second degree, aggravated assault upon a police officer or a peace officer, and assault in the first degree.

On appeal, the central issue was evidentiary and constitutional: whether the court could exclude (as irrelevant and speculative) psychiatric testimony based on a diagnosis made approximately 1½ years after the incident, where the diagnosis rested in part on pre-incident medical records and symptom history.

2. Summary of the Opinion

  • Competency to stand trial: The Fourth Department upheld the finding that the defendant was not an incapacitated person under CPL 730.10(1), concluding the People met their burden by a preponderance of the evidence that the defendant could understand the proceedings and assist counsel.
  • Preclusion of defense psychiatrist: The court reversed because the trial court abused its discretion by granting the People’s motion in limine precluding defense psychiatric testimony offered to support Penal Law § 40.15.
  • Relevance and speculation: A post-crime diagnosis can be relevant to whether the defendant suffered from a mental disease or defect at the time of the crime, particularly where the diagnosis is informed by pre-crime records and similar symptomatology.
  • Harmless error: The error was not harmless because preclusion effectively prevented the defendant from presenting the affirmative defense and severely undermined the ability to contest mens rea.
  • Disposition: Judgment unanimously reversed on the law; new trial granted.

3. Analysis

A. Precedents Cited

1) Competency standards and preservation

  • People v Mendez, 1 NY3d 15 (2003) and People v Wright, 107 AD3d 1398 (4th Dept 2013), lv denied 23 NY3d 1026 (2014): cited for the governing test and burden at a competency hearing—capacity to understand proceedings and assist in defense proved by a preponderance. These cases anchored the court’s rejection of the defendant’s challenge to the CPL 730 ruling.
  • People v Charleston, 56 NY2d 886 (1982) and People v Valle, 70 AD3d 1386 (4th Dept 2010), lv denied 15 NY3d 758 (2010): cited for preservation principles and the claim that judicial questioning transformed the judge into an advocate. The court found the issue unpreserved and, alternatively, meritless.
  • People v Prado, 4 NY3d 725 (2004), rearg denied 4 NY3d 795 (2005) and People v Tricic, 34 AD3d 1319 (4th Dept 2006), lv denied 8 NY3d 850 (2007): used to frame the asserted bias/predisposition argument as unpreserved and lacking merit.

2) The constitutional right to present a defense and evidentiary discretion

  • People v Deverow, 38 NY3d 157 (2022): supplied the overarching rule that a defendant must have a meaningful opportunity to present a complete defense, and that evidentiary discretion is “circumscribed” by that right; courts may not apply evidentiary rules “mechanistically to defeat the ends of justice.” The Fourth Department used Deverow as the constitutional lens through which it evaluated the preclusion ruling.
  • Crane v Kentucky, 476 US 683 (1986): cited for the general proposition that due process includes the right to present a complete defense.
  • People v Dixon, 42 NY3d 609 (2024), cert denied — US —, 145 S Ct 1460 (2025) (quoting Washington v Texas, 388 US 14 (1967)): emphasized that the right to offer witness testimony is a fundamental element of due process.
  • People v Sidbury, 42 NY3d 497 (2024): reinforced that restrictions on defense witnesses are scrutinized closely where truth-seeking is the goal.
  • Chambers v Mississippi, 410 US 284 (1973): supported the prohibition on rigid application of evidence rules that undermines fairness.
  • People v Carroll, 95 NY2d 375 (2000): cited for the proposition that evidentiary discretion yields where it collides with the constitutional right to present a defense.

3) The insanity (criminal responsibility) defense framework and expert evidence

  • People v Hills, 243 AD3d 1241 (4th Dept 2025): cited for the Penal Law § 40.15 standard and the defendant’s burden to prove the affirmative defense by a preponderance.
  • People v Kohl, 72 NY2d 191 (1988): confirmed that defendants bear the burden on affirmative defenses under Penal Law § 25.00(2).
  • People v Gillie, 185 AD3d 1539 (4th Dept 2020), lv denied 35 NY3d 1094 (2020): cited for the principle that, where expert evidence conflicts on criminal responsibility, the jury may accept or reject expert opinions absent a “serious flaw.” This underscored why wholesale preclusion (rather than adversarial testing before the jury) was disfavored.

4) Relevance, “speculation,” and balancing probative value versus jury confusion

  • People v Osman, 213 AD3d 1256 (4th Dept 2023): supported that improper preclusion of defense proof related to mental responsibility warrants reversal.
  • People v Morales, 125 AD2d 605 (2d Dept 1986), lv denied 70 NY2d 651 (1987): provided the key analytic template: even if an expert cannot opine on the ultimate legal question (whether the defendant met the full Penal Law § 40.15 standard at the time), the expert may still offer relevant testimony “in general terms” on the material issue of the defendant’s mental disease or defect. The Fourth Department relied heavily on Morales to reject the trial court’s “not relevant” and “speculation” rationales.
  • People v Davis, 43 NY2d 17 (1977), cert denied 435 US 998 (1978): supplied New York’s broad relevance definition—any tendency to make a consequential fact more or less probable.
  • People v McKinley, 72 AD2d 470 (4th Dept 1980): was used twice: (1) to show that a psychiatric diagnosis can be relevant to criminal responsibility, and (2) to frame the balancing rule that relevant evidence may be excluded if its probative value is outweighed by the danger of confusing the issue or misleading the jury.
  • People v Cerda, 40 NY3d 369 (2023): reinforced the modern articulation of probative-value-versus-confusion balancing.
  • People v Brown, 19 AD2d 599 (1st Dept 1963): supported the view that later psychiatric testimony may still be probative where the disorder can take time to develop and earlier records suggest pre-crime disorder, undermining the notion that the jury would necessarily be misled.

5) Harmless error and mens rea

  • People v Crimmins, 36 NY2d 230 (1975) and People v Irizarry, 248 AD2d 928 (4th Dept 1998), lv denied 92 NY2d 853 (1998): provided the harmless-error framework the court applied in determining that the evidentiary error required reversal.
  • People v Segal, 54 NY2d 58 (1981): cited to emphasize that psychiatric evidence can bear not only on the affirmative defense but also on whether the defendant formed the requisite mental state.
  • People v Vo, 166 AD3d 1587 (4th Dept 2018): supplied the “no reasonable possibility the error contributed to the verdict” formulation the court invoked to reject harmlessness.

B. Legal Reasoning

  1. Proper notice and intended use of psychiatric evidence: The defense complied with CPL 250.10 notice requirements to present psychiatric evidence tied to Penal Law § 40.15. The proposed psychiatrist would not opine on the ultimate legal conclusion but would testify to diagnosis (bipolar disorder with manic and psychotic features), its manifestations, and how pre-incident records and similar behaviors informed the diagnosis.
  2. Relevance is broad; the trial court’s “not relevant” finding was legal error: Applying People v Davis and relying on People v McKinley, the Fourth Department held that testimony establishing a diagnosis that would make a lack-of-criminal-responsibility finding “more probable” is relevant—even if diagnosis occurs post-incident—especially where based on pre-incident records and symptoms. The court emphasized that the People did not defend the “not relevant” rationale on appeal.
  3. “Speculation” concerns did not justify categorical exclusion: The court rejected the idea that the jury would necessarily speculate or be misled merely because the expert could not state the defendant’s diagnosis on the incident date. Citing People v McKinley, People v Cerda, and People v Brown, it held that the record did not support a conclusion that probative value was outweighed by confusion/misleading risk. The defense theory sought a permissible inference from the totality of evidence (before/after records and the incident behavior), not unsupported guesswork.
  4. The proper course was admission with adversarial testing, not preclusion: Echoing People v Morales, the Fourth Department stated the court should have allowed the testimony, leaving disputes about weight and inferences to the jury and ruling on specific objections to specific questions/answers as they arose.
  5. Constitutional dimension and prejudice: Through the prism of People v Deverow, People v Dixon, People v Sidbury, Crane v Kentucky, and Chambers v Mississippi, the court treated the preclusion as a serious impairment of the right to present a defense. It also stressed the practical impact: without the psychiatrist, the defendant was effectively deprived of any meaningful ability to present Penal Law § 40.15 and was severely hindered in contesting mens rea (see People v Segal).
  6. Not harmless: Applying People v Crimmins and the “reasonable possibility” standard invoked via People v Vo, the court held reversal was required because it could not say the error had no reasonable possibility of contributing to the verdict.

C. Impact

  • Clarifies relevance of post-incident psychiatric diagnoses: Trial courts in New York should treat post-crime diagnoses as potentially relevant to Penal Law § 40.15 when the diagnosis is grounded in longitudinal evidence (including pre-crime records and similar symptom patterns), even if the expert cannot pinpoint the precise diagnosis “on the date” of the offense.
  • Limits categorical preclusion based on “ultimate issue” limitations: The decision reinforces that an expert need not opine on the complete legal standard of criminal responsibility to provide admissible, relevant testimony on a component element—i.e., the existence and nature of a mental disease or defect.
  • Strengthens constitutional scrutiny of evidentiary rulings in insanity cases: By grounding the analysis in right-to-present-a-defense cases, the opinion signals that preclusion is especially disfavored where it functionally extinguishes an affirmative defense or a mens rea challenge.
  • Practical trial-management guidance: Rather than excluding the witness wholesale, courts should admit the testimony and manage risks through targeted objections, limiting instructions where appropriate, and careful control of the scope of opinions (e.g., clarifying what the expert can and cannot conclude about the time of the offense).

4. Complex Concepts Simplified

  • CPL 250.10 notice: A rule requiring advance notice when a defendant intends to introduce psychiatric evidence at trial, so the prosecution can prepare and obtain its own evaluations.
  • Penal Law § 40.15 (lack of criminal responsibility): New York’s insanity defense. Even if the defendant committed the act, they are not criminally responsible if, because of mental disease or defect at the time, they lacked substantial capacity to appreciate the nature/consequences of the act or that it was wrong.
  • Affirmative defense and burden (Penal Law § 25.00[2]): The prosecution must still prove the crime beyond a reasonable doubt, but the defendant must prove the affirmative defense by a preponderance (more likely than not).
  • Competency to stand trial (CPL 730.10[1]): A separate question from insanity: whether the defendant can understand the court process and assist counsel now, not what their mental state was during the crime.
  • Relevance: Evidence is relevant if it makes a consequential fact even slightly more or less likely (the threshold is intentionally low).
  • Probative value vs. prejudice/confusion: Even relevant evidence can be excluded if it is likely to mislead or confuse the jury more than it helps prove something important—but that balancing must be justified by the record.
  • Harmless error: Some mistakes do not require a new trial if the appellate court is satisfied the mistake did not affect the verdict. Here, because the excluded testimony went to the heart of the defense, the error was not harmless.

5. Conclusion

People v Williams establishes a practical and rights-sensitive rule for insanity-defense litigation in New York: a psychiatric diagnosis rendered after the offense may still be relevant and admissible to prove (at least) the existence of a mental disease or defect, particularly when the diagnosis is supported by pre-incident records and symptom continuity. The decision cautions trial courts against converting concerns about the limits of expert certainty into categorical preclusion—especially where doing so deprives the defendant of a meaningful opportunity to present Penal Law § 40.15 or to contest mens rea. The Fourth Department’s remedy—a new trial—signals that erroneous preclusion of core defense psychiatric evidence will rarely be treated as harmless.