Brady/Giglio Materiality Estimator

Estimate Brady/Giglio Materiality

Answer the questions below about the withheld evidence and the strength of the State’s case. The estimator applies the three-part Brady test — favorable, suppressed, and material — and returns a qualitative read: Strong, Plausible, or Weak. It runs entirely in your browser, and nothing you enter is transmitted or stored.

The Three Components of a Brady Claim

Brady v. Maryland, 373 U.S. 83 (1963), holds that the prosecution’s suppression of evidence favorable to the accused violates due process where the evidence is material to guilt or punishment, and it does so “irrespective of the good faith or bad faith of the prosecution.” The rule is not a discovery convenience; it is a constitutional floor rooted in the Fourteenth Amendment right to a fair trial.

Courts distill the doctrine into three components a defendant must establish:

1. Favorable. The evidence must help the defense — either by tending to negate guilt or reduce punishment (exculpatory) or by undercutting a prosecution witness (impeachment). United States v. Bagley, 473 U.S. 667, 676 (1985), confirms that both kinds fall within the rule.
2. Suppressed. The State must have failed to disclose the evidence, whether willfully or inadvertently. Under Kyles v. Whitley, 514 U.S. 419 (1995), the duty reaches favorable evidence known to anyone acting on the government’s behalf, including the police.
3. Material. There must be a reasonable probability that, had the evidence been disclosed, the result of the proceeding would have been different. Bagley, 473 U.S. at 682.

This tool walks the same three gates. If the first two are not met, there is no Brady claim to weigh; if they are, the tool turns to the materiality question, where most Brady litigation is actually decided.

Favorable Evidence: Exculpatory and Impeachment

Favorable evidence comes in two forms, and both trigger the disclosure duty.

Exculpatory evidence points away from guilt or toward a lighter sentence — an alternative suspect, a recantation, forensic results that do not match, or facts that mitigate punishment. In Brady itself the withheld item was a companion’s statement admitting the actual killing, which the Court held material to punishment.

Impeachment evidence attacks the credibility of a prosecution witness. Giglio v. United States, 405 U.S. 150 (1972), squarely placed impeachment inside the Brady rule. There the prosecution failed to disclose a promise of leniency to its key cooperating witness; the Court reversed, explaining that when the “reliability of a given witness may well be determinative of guilt or innocence, nondisclosure of evidence affecting credibility” falls within Brady. Bagley later confirmed that impeachment and exculpatory evidence are judged under the same materiality standard. 473 U.S. at 676.

Classic Giglio material includes plea deals and immunity agreements, pending charges that give a witness a motive to cooperate, prior inconsistent statements, and payments to informants. Giglio also reaches promises the trial prosecutor did not personally make: the Court held that a promise by one attorney in the office “must be attributed… to the Government.”

In the estimator, marking evidence as impeaching and flagging that it strikes a central witness raises the materiality read, because impeachment of a witness who may decide the case is the paradigm Giglio scenario.

Suppression, the Prosecution Team, and the Ongoing Duty

The second component asks whether the State suppressed the evidence. Several features of the duty are frequently litigated.

The prosecution team. A prosecutor cannot sidestep Brady by pointing to a colleague’s file or a detective’s notes. Kyles v. Whitley holds that “the individual prosecutor has a duty to learn of any favorable evidence known to the others acting on the government’s behalf in the case, including the police.” 514 U.S. at 437. Favorable evidence sitting in a police property room is still suppressed if it never reaches the defense.

Good faith is irrelevant. Because Brady protects the fairness of the trial rather than punishing misconduct, it applies whether the failure to disclose was deliberate or an honest oversight. Brady, 373 U.S. at 87. That is why this tool never asks about the prosecutor’s intent.

The diligence limit. Evidence is generally not “suppressed” when the defense knew of it or could have obtained it through reasonable diligence. If the defense already had the item, or a public record put it within easy reach, courts often find no suppression — and the Brady analysis stops there.

Timing and the ongoing duty. The obligation is continuing. It attaches before trial, persists through trial, and can require disclosure of newly discovered favorable evidence even after proceedings begin. Prosecutors must produce Brady material in time for the defense to use it effectively, which is why late disclosure of significant evidence can itself support relief.

Materiality: Reasonable Probability Is Not More-Likely-Than-Not

Materiality is the heart of most Brady disputes. The governing test comes from United States v. Bagley, 473 U.S. 667 (1985): evidence is material “only if there is a reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different.” A “reasonable probability” is “a probability sufficient to undermine confidence in the outcome.” Id. at 682.

Kyles v. Whitley stresses that the adjective does real work. The question is not whether the defendant would more likely than not have been acquitted with the evidence; it is whether, without it, the defendant received a trial “resulting in a verdict worthy of confidence.” 514 U.S. at 434. Four points follow from Kyles:

• Materiality is not a sufficiency-of-the-evidence test; a defendant need not show the remaining evidence was too weak to convict.
• The defendant need not prove acquittal was more probable than not.
• Materiality is measured against the whole record, not the tainted item in isolation.
• Once a court finds a Brady violation under this standard, there is no separate harmless-error review — the materiality finding already establishes prejudice. 514 U.S. at 435.

Because the standard is qualitative, this tool returns a qualitative read — Strong, Plausible, or Weak — rather than a false percentage. The strength of the State’s remaining proof is the biggest lever: the weaker the independent evidence of guilt, the more a single suppressed item can erode confidence in the verdict.

The Kyles Cumulative-Materiality Rule

A defendant rarely wins a Brady claim by isolating one withheld document. Kyles v. Whitley holds that the State’s disclosure obligation “turns on the cumulative effect of all such evidence suppressed by the government.” 514 U.S. at 421. Courts add up every item of favorable, suppressed evidence and ask whether the collection, taken together, undermines confidence in the verdict.

The practical consequences cut both ways:

• Several individually minor items can combine into a material whole. Impeachment of one witness may look trivial alone but prove decisive when layered with impeachment of a second witness and a suppressed forensic lead.
• Conversely, a single item that merely repeats impeachment the jury already heard often fails, because it adds little to the picture. That is the cumulative problem the tool flags: evidence duplicating what the defense already had rarely moves the needle.

Kyles also warns against treating each suppressed item under a separate harmless-error lens. The reviewing court makes one materiality judgment on the aggregate. When you use this estimator for a case with multiple withheld items, run the strongest combination, and treat the “cumulative” checkbox as a signal that a particular item is duplicative of proof already in hand.

The Texas Overlay: Article 39.14(h) and the Michael Morton Act

Texas gives defendants a statutory disclosure right that is broader than federal Brady. The Michael Morton Act rewrote Tex. Code Crim. Proc. art. 39.14, and subsection (h) provides that “the state shall disclose to the defendant any exculpatory, impeachment, or mitigating document, item, or information in the possession, custody, or control of the state that tends to negate the guilt of the defendant or would tend to reduce the punishment.”

Two differences matter for practice:

No materiality threshold.

Article 39.14(h) is not conditioned on a “reasonable probability of a different result.” The State must turn over exculpatory, impeachment, and mitigating information without the defense first proving it would change the outcome. Materiality still governs the constitutional remedy after conviction, but the statutory duty to disclose is triggered earlier and more broadly.

An ongoing, self-executing duty.

The obligation runs throughout the case and, for exculpatory or mitigating information, does not depend on a defense request for the specific item. Article 39.14 also requires disclosure of much of the State’s file on a timely request, backed by discovery procedures the federal system lacks.

For a Texas case, then, a favorable, suppressed item can support a statutory violation under article 39.14 even where the federal materiality showing is a close call. This tool applies the constitutional Brady/Giglio materiality test; treat a “Weak” or “Plausible” read as a reason to press the broader Texas statutory duty as well.

Where the Brady Motion and the New-Trial Motion Fit

The right vehicle depends on when the favorable evidence comes to light.

• Before or during trial. File a Brady/Giglio disclosure motion to compel production and, where needed, to seek a continuance or in-camera review. In Texas, pair it with a discovery demand under article 39.14.
• After a guilty verdict, within the deadline. Move for a new trial. In federal court that is a Rule 33 motion, which allows a longer window when the ground is newly discovered evidence. In Texas, a motion for new trial must be filed within 30 days after sentence under Texas Rule of Appellate Procedure 21.4.
• After the new-trial deadline. A Brady claim can still be raised by writ of habeas corpus — in Texas under article 11.07 (felony) or 11.072, and federally under 28 U.S.C. 2254 or 2255 — because a due-process violation is cognizable on collateral review.

Whatever the posture, the pleading must connect the three components to the record: identify the favorable evidence, show it was in the State’s possession and not disclosed, and explain — cumulatively — why its absence undermines confidence in the verdict under Bagley and Kyles. The estimator is a triage aid for that showing, not a substitute for counsel’s record-specific judgment.

The Case Law Behind This Tool

The controlling decisions this tool is built on—each verified against the published opinion. Holdings are neutral summaries of the law, not predictions about any case.