Date: Jun 12, 2026

State v. Montgomery (2026 N.H. 24): Severance Required Where Joinder Creates Propensity-Risk, and “Intrinsic” Evidence Has Narrow Limits

Introduction

In State v. Montgomery, 2026 N.H. 24 (N.H. June 11, 2026), the Supreme Court of New Hampshire reviewed a multi-count prosecution arising from the death of five-year-old Harmony Montgomery and the defendant’s conduct before and after her death. The defendant, Adam Montgomery, was convicted after a single jury trial of: second degree murder (RSA 630:1-b, I(b)); second degree assault for an earlier alleged assault in July 2019 (RSA 631:2, I(d)); falsifying physical evidence (RSA 641:6, I); witness tampering (RSA 641:5, I(a)); and abuse of a corpse (RSA 644:7).

The appeal principally raised (1) whether the trial court erred by refusing to sever the July 2019 assault charge from the December 2019 homicide-related charges under New Hampshire Rule of Criminal Procedure 20’s “best interests of justice” standard; and (2) whether certain “other act” evidence was properly treated as “intrinsic” (and therefore outside New Hampshire Rule of Evidence 404(b)); and (3) whether a silent video of a 2021 police encounter improperly conveyed constitutionally protected silence or was irrelevant/unfairly prejudicial.

The Supreme Court affirmed the assault, falsifying physical evidence, witness tampering, and abuse-of-a-corpse convictions, but reversed the second degree murder conviction and remanded.

Summary of the Opinion

Severance: Even assuming joinder was permissible initially, the Court held the “best interests of justice” required severance because the strong July-assault evidence (multiple witnesses and admissions) created a substantial risk the jury would use it for an impermissible propensity inference when deciding the materially weaker murder case, which depended largely on Kayla Montgomery’s credibility. The limiting instruction given did not address the core risk because it did not tell jurors they could not use evidence from one charge to decide another. The misjoinder was harmless as to the assault conviction but not harmless as to the murder conviction.
Other-acts as “intrinsic” evidence: Evidence of the defendant striking the victim during the family’s homelessness shortly before the charged homicide was properly admitted as intrinsic because it was part of the course of conduct leading to the charged offense and completed the story. In contrast, evidence that the defendant prevented the victim’s mother from contacting the victim for months was not intrinsic to the murder; if admissible, it must be evaluated under Rule 404(b).
Silent police-encounter video: The no-audio video did not constitute impermissible evidence of pre-arrest silence and, though only slightly probative, posed virtually no danger of unfair prejudice under Rules 402 and 403.

Analysis

Precedents Cited

1. Joinder, severance discretion, and the “best interests of justice”

The Court framed review as discretionary and reversible only for an unsustainable exercise of discretion, relying on State v. Girard, 173 N.H. 619 (2020). It interpreted Rule 20 through prior joinder doctrine in State v. Brown, 159 N.H. 544 (2009), including the recognized danger that “a weak case” can be unfairly bolstered by joinder with “a strong case” through the “accumulated effect of the evidence.”

For the operative severance standard, the Court leaned on State v. Rivera, 175 N.H. 496 (2022), emphasizing that separate trials are warranted when a single trial jeopardizes a fair determination of guilt/innocence and when the factfinder may be unable to compartmentalize evidence and law across counts—especially where inflammatory spillover, disparate proof strength, or inconsistent defenses are present.

2. Limiting instructions and when they fail to cure joinder prejudice

The State invoked the general presumption that juries follow instructions, citing State v. Manna, 130 N.H. 306 (1988), and the Court acknowledged the principle as reiterated in State v. Mason, 150 N.H. 53 (2003). But Mason also supplies the counterweight: sometimes prejudice is likely enough that the presumption is overcome. Here, the Court found the instruction inadequate because it told the jury to consider indictments separately but did not prohibit using evidence from one count to decide another, leaving the central propensity pathway open.

3. Propensity inferences from joinder: persuasive authority

The Court illustrated the propensity-spillover mechanism with federal persuasive authority, Bean v. Calderon, 163 F.3d 1073 (9th Cir. 1998), describing how joinder can enable an impermissible inference of criminal propensity that strengthens an otherwise weak case.

4. Waiver/forfeiture of appellate arguments based on trial-level concessions

On the State’s argument that the defendant’s earlier assent to joinder should foreclose relief, the Court relied on Milliken v. Dartmouth-Hitchcock Clinic, 154 N.H. 662 (2006), refusing to consider an appellate argument the State had disclaimed below (the State had conceded the defendant could withdraw assent and obtain a fresh “best interests” analysis).

5. Harmless error for misjoinder

The harmless-error framework was taken from State v. Rouleau, 176 N.H. 400, 2024 N.H. 2, which enumerates a multi-factor totality test. The Court also referenced Tabish v. State, 72 P.3d 584 (Nev. 2003), for the proposition that improper joinder may be harmless as to strong counts yet prejudicial as to weak ones. It contrasted State v. Cossette, 151 N.H. 355 (2004), where mixed verdicts can evidence jury compartmentalization; here, all-guilty verdicts did not provide that assurance.

6. “Intrinsic” vs Rule 404(b) other-acts evidence

The intrinsic-evidence doctrine was grounded in State v. Thomas, 168 N.H. 589 (2016), and refined through State v. Rouleau, 176 N.H. 400, 2024 N.H. 2, which describe intrinsic evidence as “inextricably intertwined” with the charged offense, typically with causal/temporal/spatial connection, and serving to complete the story. The Court assessed the “factual nexus” concept using State v. Papillon, 173 N.H. 13 (2020), which warns that temporal proximity alone is insufficient.

For the admissibility rationale that juries are entitled to understand the immediate context (events do not occur in a vacuum), the Court relied on State v. Wells, 166 N.H. 73 (2014), which also highlights that context evidence can materially aid jurors’ assessment of whether the charged conduct occurred.

For the proposition that evidence undermining a defendant’s account is typically treated under Rule 404(b) rather than as intrinsic, the Court cited State v. Dukette, 145 N.H. 226 (2000).

7. Pre-arrest silence and police encounter evidence

The defendant’s constitutional challenge referenced State v. Remick, 149 N.H. 745 (2003), recognizing that using pre-arrest silence in the State’s case-in-chief (when a defendant does not testify) is unconstitutional under the Fifth Amendment. The Court distinguished the silent video from “silence” evidence because the video did not depict an invocation or noncooperation in a way likely to invite jury speculation.

Legal Reasoning

A. Why severance was required under Rule 20’s “best interests of justice”

The Court’s severance analysis turned on the interaction between (1) the relative evidentiary strength of the two assaults (July 2019 vs. December 2019 homicide), (2) the similarity of the alleged conduct (striking the same child victim, including blows to the head), and (3) the defense theory that Kayla (not the defendant) caused the fatal injury. The July assault was supported by multiple witnesses who observed a black eye and multiple admissions by the defendant. The murder charge, by contrast, hinged on Kayla’s testimony as the only direct account of the fatal blows, and her credibility was heavily contested due to perjury convictions and other impeachment material.

Although the State offered substantial corroboration for post-death concealment (DNA, fingerprints, receipts, witness testimony about storage/disposal), the Court emphasized that this corroboration did not meaningfully corroborate who inflicted the fatal injuries and was consistent with the defense theory that the defendant helped conceal a death caused by Kayla. In this posture, the Court viewed joinder as creating an acute propensity risk: jurors could reason that because the defendant had assaulted the victim before, he was more likely to have assaulted her fatally.

The Court found the trial court’s limiting instruction misaligned with the identified prejudice. Telling jurors to consider indictments separately does not necessarily prevent them from using evidence from one indictment as proof in another. Because the key risk was cross-count propensity use, an instruction would have had to address that specific use (i.e., prohibit using July-assault evidence to infer the defendant’s identity as the killer). The absence of such a directive left the principal joinder harm uncured.

B. Harmlessness applied count-by-count

Applying Rouleau’s totality factors, the Court treated the misjoinder’s effect as asymmetric. The July assault conviction stood because the State’s case on that count was independently strong; the murder conviction fell because the joint trial plausibly supplied the missing link in a weak-identity case through impermissible character reasoning. Importantly, the Court rejected the State’s “overwhelming evidence” characterization because much of the strongest evidence related to concealment-related counts, not the contested mechanism and perpetrator of the fatal assault.

C. Intrinsic evidence: course-of-conduct versus remote narrative

For homelessness-period assaults shortly before December 7, the Court identified a tight factual nexus: same victim, similar trigger (incontinence), same mechanism (punching/striking), and close temporal/spatial proximity while living in the car. This evidence was treated as part of the “course of conduct” leading to the charged homicide and as “prelude”/“story completion” evidence under Rouleau and Wells.

By contrast, “interference with mother’s contact” evidence lacked the necessary causal, temporal, or spatial connection to the homicide and did not meaningfully “complete the story of the charged offense.” That it might explain how the mother came to contact law enforcement, or that it undercut an alternative narrative, did not convert it into intrinsic evidence. The Court’s key doctrinal move is to confine “intrinsic” status to evidence connected to the charged offense itself, not merely helpful to rebut a defense story in a broader sense.

D. Police-encounter video: minimal probative value but minimal prejudice

The Court credited the defendant’s successful exclusion of actual statements after invocation, but held that the silent video itself did not communicate an invocation or noncooperation. It therefore did not operate as unconstitutional pre-arrest silence evidence under Remick. The remaining evidentiary analysis under Rules 402 and 403 was pragmatic: slight probative value (investigative context, whereabouts) and virtually no unfair prejudice.

Impact

Sharper severance scrutiny when a strong “prior assault” count is joined to a weak “fatal assault” identity case. Trial courts should treat joinder as especially risky when the joined counts invite a straightforward propensity inference (same victim, similar conduct), and when the contested count depends on a single compromised witness.
Limiting instructions must match the actual spillover theory. A generic “consider each indictment separately” instruction may be inadequate where the danger is cross-count use of evidence (not merely confusion between indictments). Montgomery signals that courts should consider whether jurors are being told, expressly, what they may not do with the evidence.
Count-specific harmless error analysis in misjoinder cases. The decision reinforces that misjoinder can be harmless for some convictions but reversible for others—encouraging litigants and courts to evaluate prejudice with granularity, not globally.
Narrowing the “intrinsic evidence” label. The Court’s treatment of “interference with mother’s contact” evidence limits the State’s ability to bypass Rule 404(b) by characterizing context evidence as intrinsic when it lacks a close connection to the charged crime. On retrial, prosecutors should expect to justify such evidence under Rule 404(b) (proper purpose, relevance, Rule 403 balancing, and limiting instructions).

Complex Concepts Simplified

Joinder vs. severance (Rule 20): “Joinder” means trying multiple charges in one trial. “Severance” means splitting them into separate trials. Even if charges can be joined, the court must sever if one trial would be unfair—especially if evidence from one count could improperly sway the jury on another.
Propensity evidence: Evidence used to argue “he did it before, so he did it again.” The law generally forbids this reasoning because it can lead jurors to convict based on character rather than proof beyond a reasonable doubt of the charged act.
Intrinsic evidence vs. Rule 404(b) “other acts”: “Intrinsic” evidence is so closely connected to the charged crime (same episode, direct lead-up, necessary to understand what happened) that it is treated as part of the story of the charged offense itself. Other-acts evidence that is not intrinsic must satisfy Rule 404(b): it cannot be used to show propensity, but may be allowed for other legitimate reasons (motive, intent, identity, etc.) if its probative value is not substantially outweighed by unfair prejudice.
Harmless error: Even if the trial court made a mistake, the conviction stands if the State proves beyond a reasonable doubt that the mistake did not affect the verdict. In misjoinder cases, this can differ by count: an error may not matter for a strongly proven charge but may matter greatly for a close, credibility-driven charge.
Zwicker letter: The opinion notes that a “Zwicker letter”—a term used colloquially in New Hampshire practice, loosely based on State v. Zwicker, 151 N.H. 179 (2004)—refers here to the State’s written disclosure of newly discovered evidence not previously included in Rule 12(b)(1) disclosures.

Conclusion

State v. Montgomery establishes a practical but consequential clarification of New Hampshire criminal procedure and evidence: when joinder of a strong prior-assault count with a weaker homicide identity case creates a substantial propensity-risk, Rule 20’s “best interests of justice” requires severance, and generic “separate indictments” instructions may not cure the prejudice. The decision also tightens the boundary of “intrinsic” evidence, permitting close-in-time course-of-conduct evidence while rejecting a broader narrative approach that would evade Rule 404(b). On remand, the State may retry the murder charge, but must do so without the unfair spillover that the Court identified and with careful attention to the proper evidentiary pathway for non-intrinsic other-acts evidence.