Is failure to comply with Brady Rules cause for a mistrial?
<p><a href="https://www.law.cornell.edu/wex/brady_rule#:%7E:text=The%20Brady%20Rule%2C%20named%20after,government%27s%20possession%20to%20the%20defense." rel="nofollow noreferrer">The Legal Information Institute defines the Brady Rule as follows.</a></p>
<blockquote>
<p>Brady Rule Primary tabs The Brady Rule, named after Brady v. Maryland,
373 U.S. 83 (1963), requires prosecutors to disclose materially
exculpatory evidence in the government's possession to the defense. A
&quot;Brady material&quot; or evidence the prosecutor is required to disclose
under this rule includes any evidence favorable to the
accused--evidence that goes towards negating a defendant's guilt, that
would reduce a defendant's potential sentence, <strong>or evidence going to
the credibility of a witness.</strong></p>
</blockquote>
<p>In regards to the issue of a credibility check of a witness. I f the government withholds information that is pertinent to the credibility of a witness is that cause for a mistrial? Does whether the government knowingly or unknowingly withheld this information influence whether a mistrial will be granted?</p>

<blockquote>
<p>If the government withholds information that is pertinent to the
credibility of a witness is that cause for a mistrial?</p>
</blockquote>
<p>Only if the error is not harmless under the standard applicable to evaluating harmless error in criminal cases (there is a voluminous case law on that point). Basically, it means that a new trial may be held and a conviction vacated on a charge against a particular defendant if there is a reasonable possibility that the withheld evidence, when considered in light of the total picture of evidence presented at trial, might have changed the outcome on guilt or innocence.</p>
<blockquote>
<p>Does whether the government knowingly or unknowingly withheld this
information influence whether a mistrial will be granted?</p>
</blockquote>
<p>Not really. Knowledge is imputed. If someone in the prosecution team including the police knows, then it is known to the entire team for <em>Brady</em> purposes.</p>
<p>If no one knew that it had the information (e.g. a key exculpatory document in possession of the prosecution was misfiled in one of dozens of bankers boxes of documents that it seized in a search and no one reviewed those particular boxes knowing to look for a document like that one or attuned to its potential significance, since it wasn't supposed to be in the place where it was filed), then it hasn't been withheld in the <em>Brady</em> sense unless someone specifically asked for the information in question with enough specificity that it could have been located if they looked at what they already had.</p>
<p>The knowledge that must be disclosed is what the <a href="https://en.wikipedia.org/wiki/Brady_disclosure" rel="nofollow noreferrer">prosecutor's office or the police the prosecutor's office is working with knows</a>. So, if a beat cop hides exculpatory evidence from the prosecutor's office, that is a <em>Brady</em> violation, but if the cops do a sloppy investigation that fails to reveal exculpatory evidence that is out there to be found, it isn't a <em>Brady</em> violation. Likewise, if a cop in another department halfway across the state knows something that impacts the credibility of a witness and the prosecutor is totally unaware of the existence of that information as are all the cops working on the case, then that isn't a <em>Brady</em> violation.</p>
<p><strong>What If It Isn't A <em>Brady</em> Violation?</strong></p>
<p>Exculpatory evidence discovered after the trial that isn't a <em>Brady</em> violation not to disclose may still be grounds for a new trial based upon newly discovered evidence in a motion for post-trial relief.</p>
<p>But, the standard to get the court to grant a new trial based upon newly discovered evidence that was not withheld in a <em>Brady</em> violation is much more stringent than the mere harmless error standard. <a href="https://www.supremecourt.gov/DocketPDF/19/19-230/112780/20190819140612493_Prade%20v.%20Ohio%20-%20Cert%20Petition.pdf" rel="nofollow noreferrer">Instead</a>:</p>
<blockquote>
<p>With a single exception, criminal defendants in the United States
seeking a new trial based on newly discovered evidence are required to
establish only that the new evidence makes it more likely than not
that, in a new trial, they would be acquitted.</p>
</blockquote>
<p>Ohio requires clear and convincing evidence rather than a mere preponderance.</p>
<p>There's a lot of case law on what constitutes newly discovered evidence which is &quot;new, material evidence that was unavailable at the time of the original trial[.]&quot; If evidence was available, but not used at trial, it can't be presented in a motion for new trial based upon newly discovered evidence. Often this means that it can't be considered even if the salience of the evidence previously available is only clear later in the light of other evidence that is genuinely newly discovered, or the defense attorney's failure to use that evidence in the first trial was negligent to a level constituting legal malpractice.</p>

united-states witnesses