Clarifying Brady’s “Reasonable Probability” Standard and the Use of Supervisory Control to Prevent a Second Trial Under a Mistake of Law

Introduction

This supervisory-control proceeding arises from a Yellowstone County criminal prosecution involving a fatal pedestrian–vehicle impact. The State’s forensic pathologist, Dr. Kemp, disclosed at trial a new speed-causation opinion based on a forensic textbook that had not been provided to the defense prior to trial. After the verdict, defense counsel discovered an email Dr. Kemp sent the prosecution identifying the textbook and quoting it—but omitting limiting language that undermined the State’s speed theory and supplied impeachment and exculpatory content.

The District Court granted a new trial for statutory discovery violations under Montana’s criminal discovery statutes (MCA §§ 46-15-322, -327), but denied Wegner’s separate request to set aside the verdict and dismiss with prejudice based on Brady v. Maryland, reasoning it was “not entirely certain” disclosure would have changed the outcome. Wegner petitioned the Montana Supreme Court for supervisory control, arguing that the District Court applied the wrong legal standard to Brady’s third prong (materiality), and that forcing a second trial while a constitutional error remained unresolved would work a gross injustice.

In its September 23, 2025 order, the Montana Supreme Court granted supervisory control, held that the District Court had already found Brady’s first two prongs satisfied, and remanded for the District Court to clarify its ruling under the correct “reasonable probability” standard for Brady materiality. The Court took no position on whether dismissal would be an appropriate remedy if a Brady violation is found, but emphasized that dismissal is reserved for egregious or outrageous government conduct.

Summary of the Opinion

The Supreme Court granted Wegner’s petition for a writ of supervisory control.
It held that the District Court had already determined (1) the State possessed evidence favorable to the defense (Dr. Kemp’s email and the underlying textbook reference), and (2) the State suppressed it by not disclosing before trial.
The Supreme Court concluded that the District Court’s denial of dismissal appeared to apply a more demanding standard (“entire certainty”) than Brady requires for the third prong (materiality) and remanded for clarification using the correct “reasonable probability” standard from State v. Severson, 2024 MT 76.
The Court reaffirmed that dismissal is a “severe sanction” not the default remedy for Brady violations, reserved for “egregious” or “outrageous” government conduct (State v. Schauf, 2009 MT 281).
The Court accepted supervisory control in this context to avoid a second criminal trial proceeding under a potential mistake of law causing gross injustice, a recognized but limited use of the writ. It reiterated that supervisory control is not a substitute for appeal (Yellowstone Electric; Hartman) but exercised the writ here given the constitutional stakes and timing.
The Court also underscored a procedural guardrail: without cross-petitioning, the State could not expand the issues beyond the question Wegner presented (i.e., the third Brady prong and remedy), especially where doing so would deprive the petitioner of a chance to respond.

Detailed Analysis

Factual and Procedural Background

Before trial, Dr. Kemp’s autopsy report noted a 12-centimeter tear in the decedent’s left femoral region but did not opine on vehicle speed. In a trial-preparation interview days before trial, Dr. Kemp told the State he had reviewed literature suggesting femoral-tear injuries “usually” occur at impacts above approximately 60 mph and “never” below 30 mph. He followed up by email identifying the forensic textbook and including a quotation. The State did not disclose this development or the email. At trial, the court allowed Dr. Kemp to testify, after voir dire, that femoral-tear injuries do not occur below about 30 mph and usually occur around 60 mph. On questioning, he added that if forced to choose, he would say the vehicle was going “faster rather than slower.”

After trial, defense counsel discovered Dr. Kemp’s email and obtained the textbook. Counsel learned that the portion Dr. Kemp quoted omitted qualifying language indicating that higher-speed impacts causing femoral-region tears often produce amputations and a somersaulting trajectory—features absent here. Counsel also found statements in the same source undercutting speed-from-injury inferences, e.g., “there is no reliable method for evaluating crash speed in terms of biological markers” and that attempts to correlate injury severity to crash speed have yielded no reliable methods of crash-speed determination. The defense moved for a new trial based on statutory discovery violations and separately to set aside the verdict and dismiss with prejudice for a Brady violation.

The District Court granted a new trial for the statutory violation—finding the State had an affirmative duty to disclose Dr. Kemp’s changed opinion, his email, and the literature underlying it, and that the nondisclosure prejudiced Wegner. But it denied dismissal on the Brady claim, stating it was “not entirely certain” disclosure would have changed the outcome, and that the situation did not undermine confidence in the verdict enough to “require dismissal.” Wegner then sought supervisory control on the ground that a second trial would proceed under an unresolved mistake of law on a constitutional claim.

Precedents Cited and Their Influence

State v. Severson, 2024 MT 76, ¶ 16: The Court relied on Severson for Brady’s three-pronged test—(1) favorable evidence; (2) suppression by the State; and (3) materiality measured by whether there is a reasonable probability of a different result, meaning a probability sufficient to undermine confidence in the outcome. Severson anchors the “reasonable probability” standard the Supreme Court instructed the District Court to apply on remand.
State v. Schauf, 2009 MT 281, ¶ 26: Cited to emphasize that dismissal of criminal charges is a severe and disfavored remedy for disclosure failures, reserved for egregious or outrageous government conduct. This circumscribes the remedy analysis that may follow if the District Court finds a Brady violation on remand.
Yellowstone Elec. Co. v. Mont. Seventh Jud. Dist. Ct., No. OP 19-0348, 397 Mont. 552, 449 P.3d 787 (Aug. 6, 2019), and Hartman v. Mont. Nineteenth Jud. Dist. Ct., No. OP 20-0069, 399 Mont. 551, 460 P.3d 400 (Feb. 11, 2020): These decisions restate that supervisory control is not a shortcut around ordinary appellate processes. The Court distinguished this case from those, holding that the risk of a second criminal trial proceeding under a potential mistake of law on a constitutional matter warranted intervention.
Disability Rights Mont. v. Mont. Jud. Dists. 1–22, No. OP 20-0189, 400 Mont. 556 (Apr. 14, 2020), citing Miller v. 11th Jud. Dist. Ct., 2007 MT 58, ¶ 14, 336 Mont. 207, 154 P.3d 1186: The Court invoked these authorities to confirm that the petitioner bears the burden to justify the extraordinary writ—a burden Wegner met. The Court’s acceptance of supervisory control underscores both the gravity of constitutional error and the efficiency in correcting it before retrial.

The Court’s Legal Reasoning

Supervisory control in a pre-retrial posture: The Court acknowledged its consistent caution against using supervisory control merely to conserve resources. But it recognized an exception where allowing a second criminal trial to proceed under an unresolved constitutional issue, coupled with an apparent mistake of law by the District Court, risks a gross injustice. That combination satisfied the threshold for issuing the writ in this case.
Brady’s first two prongs were satisfied below: Contrary to the State’s characterization, the District Court found that Dr. Kemp’s email and the associated information were “material and favorable to the defense” and that the State possessed and suppressed this information before trial. The Supreme Court treated those determinations as established for purposes of this writ proceeding. It further admonished that, absent a cross-petition, the State could not expand the issues to contest those findings in this supervisory-control posture.
Correct materiality standard under Brady: The Supreme Court’s central holding is that the District Court must apply the “reasonable probability” standard to Brady’s third prong: whether the undisclosed evidence is material in the sense that its nondisclosure undermines confidence in the verdict. The District Court’s phrasing—“not entirely certain” that disclosure would have changed the outcome—suggested a more-onerous “certainty” or “more likely than not” threshold, which is not the Brady standard. Because the District Court also granted a new trial on statutory-disclosure grounds, its order contained language that could be read either way; the Supreme Court therefore remanded solely for clarification under the proper standard.
Remedy is not predetermined: The Court explicitly declined to determine the appropriate remedy if the District Court finds a Brady violation on remand. It reiterated that dismissal is a severe and rarely appropriate remedy, reserved for egregious or outrageous prosecutorial conduct (Schauf), and is not the “remedy of choice.” Given that a new trial has already been ordered for statutory violations, the District Court retains discretion to determine whether, if a Brady violation is established under the correct standard, the remedy should exceed a new trial.

Impact and Practical Implications

For trial courts: This decision is a pointed reminder to apply the correct Brady materiality test—reasonable probability of a different result, not certainty or preponderance. Orders should make that standard explicit, particularly where a statutory discovery violation has already been found, to avoid conflating statutory prejudice with constitutional materiality.
For prosecutors:
- Affirmative and ongoing disclosure duties under MCA §§ 46-15-322 and -327 extend to late-developed expert opinions and their bases, including literature consulted during trial preparation. A failure to promptly disclose can itself warrant a new trial.
- Brady obligations include impeachment evidence and information that points the defense to impeachment sources. When the State has an email identifying a source and quoting selectively, courts may treat that as favorable evidence in the State’s possession, especially where the omitted portions are exculpatory or impeaching.
- Do not assume that information in public sources (e.g., textbooks) falls outside Brady; the duty is to disclose favorable evidence in the State’s possession or known to its team, including pointers to material that the State itself has consulted.
- In writ practice, respondents must either confine arguments to the issues framed by the petition or cross-petition; raising new issues risks procedural rebuke and may be disregarded.
For defense counsel:
- When experts change opinions or consult new literature close to trial, seek immediate disclosure of the opinion, bases, and communications memorializing them. If disclosure lapses, preserve both statutory-discovery and Brady objections and remedies.
- Brady’s materiality need not show that a different result is “more likely than not,” only that nondisclosure undermines confidence in the verdict. Target this standard in briefing and seek explicit application by the trial court.
- Impeachment material—particularly literature that undermines the methodology or conclusions of a State’s expert—qualifies as “favorable” under Brady.
- In appropriate cases, consider supervisory control to prevent a second trial from proceeding under a legal error that cannot be adequately remedied on appeal after retrial.
On expert testimony about crash speed from injury patterns: The factual record highlights literature stating there is “no reliable method for evaluating crash speed in terms of biological markers” and that injury-severity correlations are not reliable for speed estimation. This may have ramifications for Rule 702/Daubert-style gatekeeping in Montana courts when experts attempt to infer vehicle speed from injury morphology—an issue trial courts should scrutinize on remand if the testimony is reoffered.
Procedural practice in writ proceedings: The Court’s admonition that the State could not broaden the issues without a cross-petition is a useful procedural marker: in supervisory-control cases, the respondent risks forfeiture of broader challenges not encompassed within, or noticed for, the writ.

Complex Concepts Simplified

Brady violation: A constitutional rule requiring the prosecution to disclose, before trial, evidence favorable to the accused. To prove a violation, a defendant must show: (1) the State possessed evidence favorable to the defense (including impeachment material); (2) the State suppressed that evidence; and (3) there is a reasonable probability that, had it been disclosed, the outcome would have been different—i.e., nondisclosure undermines confidence in the verdict.
“Reasonable probability” vs. “certainty”: “Reasonable probability” is less than “more likely than not.” It asks whether the undisclosed evidence is significant enough to cast doubt on the reliability of the verdict, not whether it would definitively flip the outcome.
Statutory discovery vs. Brady: Montana’s discovery statutes (MCA §§ 46-15-322, -327) impose affirmative, continuing duties to disclose specified categories of information, including new opinions and the bases of expert testimony. Violations can warrant sanctions, including a new trial, even when the constitutional Brady standard is not met. Brady is a constitutional floor; statutory rules can be stricter.
Supervisory control (writ): An extraordinary remedy the Montana Supreme Court uses sparingly to control lower-court proceedings. It is not a replacement for appeal. It may be granted when a lower court is proceeding under a mistake of law that risks causing gross injustice, as when a second criminal trial might occur under an unresolved constitutional error.
Dismissal as a remedy: Throwing out criminal charges for disclosure violations is a last resort, typically reserved for egregious or outrageous government misconduct. More common remedies include a new trial, exclusion of evidence, or other sanctions.
Impeachment evidence: Information used to challenge a witness’s credibility, qualifications, or methodology (e.g., literature contradicting an expert’s conclusions). Such evidence is “favorable” under Brady and must be disclosed if possessed by the State.

Conclusion

This decision accomplishes two important clarifications. First, it underscores that Brady’s materiality turns on a “reasonable probability” of a different result—an inquiry into whether nondisclosure undermines confidence in the verdict, not whether a different outcome is certain or more likely than not. Second, it delineates a judicious use of supervisory control in the criminal context: the writ may issue to prevent a second trial from going forward under a potential misapplication of constitutional law that could cause gross injustice.

Practically, the case warns prosecutors to promptly disclose late-breaking expert opinions and the underlying literature, reinforces that impeachment material is “favorable” under Brady, and cautions trial courts to apply the correct constitutional standard distinctly from statutory discovery analyses. It also signals that respondents in writ proceedings should not expand the scope of issues without cross-petitioning. On remand, the District Court must clarify whether, under the correct “reasonable probability” standard, the nondisclosure of Dr. Kemp’s email and the associated literature was material—and, if so, determine the appropriate remedy consistent with Montana law and Schauf’s admonitions regarding dismissal.

In the broader legal landscape, Wegner strengthens the fidelity of Montana courts to Brady’s materiality standard and models a restrained but decisive use of supervisory control to correct pivotal legal standards before retrial, thereby promoting both fairness and judicial economy in criminal proceedings.