A mistrial is what a judge declares when something goes so wrong during a trial that no instruction can fix it, forcing the proceedings to end before a verdict. The three things that cause a mistrial most often are a jury that cannot reach a unanimous decision, misconduct by a juror, lawyer, or witness, and emergencies that make continuing impossible. A mistrial does not acquit the defendant. In most cases, the prosecution can start the whole trial over.
A Jury That Cannot Agree
A hung jury is the single most common trigger. The Sixth Amendment requires a unanimous verdict for any serious criminal offense in both federal and state courts, which the Supreme Court confirmed in Ramos v. Louisiana. One holdout is enough to stall everything.1Constitution Annotated. Amdt6.4.4.3 Unanimity of the Jury
When jurors say they are stuck, the judge usually does not end things right away. The standard response is a supplemental instruction asking them to go back and genuinely reconsider the evidence and each other’s reasoning. It is called an “Allen charge,” named for the 1896 Supreme Court decision in Allen v. United States. The Court approved language telling dissenting jurors to ask themselves whether their doubt is reasonable if it fails to persuade equally honest and intelligent peers, while also asking the majority to seriously consider whether the minority might be right.2Justia Law. Allen v. United States, 164 U.S. 492 (1896)
Allen charges draw criticism because they can push minority jurors into caving instead of holding to a sincere belief. Several states restrict or forbid them. Where they are allowed, the instruction generally has to remind jurors that no one should abandon an honestly held conviction simply to produce a verdict, and judges cannot cite the cost or inconvenience of a retrial as motivation. If the deadlock holds after that, the judge declares a mistrial.
Juror Misconduct
Jurors are supposed to decide the case using only what they hear in the courtroom. When one of them steps outside that boundary, the contamination can force a mistrial. The Sixth Amendment guarantees a jury free from outside influence, and the Supreme Court has held that judges must investigate whenever a juror may have been exposed to prejudicial material or improper contact.3Constitution Annotated. Amdt6.4.5.2 Jury Free from Bias
The behaviors that most often derail trials include researching the case online, visiting the scene of the alleged crime on their own, discussing the case with family or friends before deliberations end, and consuming news coverage after the judge told them not to.
Internet research is the biggest modern problem. A juror who searches for news about the defendant, looks up a witness’s background, or Googles a legal term brings in evidence neither side had any chance to challenge, which is exactly the kind of outside influence the Sixth Amendment prohibits.3Constitution Annotated. Amdt6.4.5.2 Jury Free from Bias
A juror who lies during jury selection creates a different problem with the same ending. If someone conceals a bias or personal connection to the case and the truth emerges mid-trial, the judge may have to start over because the jury was never actually impartial to begin with.
Attorney and Witness Misconduct
Lawyers can poison a trial too. The patterns that most often lead to mistrials are inflammatory arguments that go beyond the evidence (such as appealing to racial bias or accusing a defendant of uncharged crimes), repeated attempts to introduce evidence the judge has already excluded, and conflicts of interest. On that last one, the Supreme Court has recognized that an actual conflict affecting a defense lawyer’s performance violates the Sixth Amendment right to effective counsel, and a judge who discovers such a conflict mid-trial may call a halt rather than let a constitutionally defective proceeding continue.4Constitution Annotated. Amdt6.6.5.3 Deprivation of Effective Assistance of Counsel in Joint Representation
Witnesses cause mistrials less often, but when they do it tends to be dramatic. The classic example is a witness blurting out that the defendant has a prior criminal record. Evidence rules generally bar using someone’s past convictions to argue they must have committed the current offense, because juries give that kind of information far more weight than it deserves. One offhand remark from the stand can undo weeks of careful preparation.
Why Some Errors Do Not End the Trial
Judges do not reach for a mistrial every time something goes wrong. The first tool is a curative instruction, where the judge tells the jury to disregard what they just heard and explains why. For an isolated, unintentional slip, a prompt and specific instruction is usually enough. Courts treat a mistrial as a drastic remedy.
The line between fixable and unfixable comes down to how severe the error was, whether it was repeated, and whether it was deliberate. A passing reference to excluded information is different from a vivid, detailed revelation the jury heard clearly and cannot unhear. When the prejudicial material is central to the case, telling twelve people to forget it is asking the impossible, and a mistrial becomes the only honest option. A prosecutor who deliberately provoked the moment also faces a harsher standard than a witness who made a genuine mistake.
Emergencies and Jurisdictional Defects
Some mistrials have nothing to do with anyone’s behavior. The death or sudden incapacitation of a key participant, such as a juror, the presiding judge, or lead counsel, can make continuing impossible. If enough alternate jurors are available, losing one juror might not end things. When the trial cannot lawfully proceed with who remains, the judge has no choice.
Other triggers include natural disasters that close the courthouse, a public health emergency that halts proceedings, or the discovery mid-trial that the court lacks jurisdiction over the case. Jurisdictional defects are especially serious. If the court has no legal authority over the subject matter or the parties, any verdict would be void, and the judge has to stop immediately.
Can You Be Retried After a Mistrial?
Usually, yes. The Fifth Amendment’s Double Jeopardy Clause says no person can be tried twice for the same offense, but the Supreme Court held nearly two centuries ago in United States v. Perez that a judge may discharge a jury and allow retrial whenever there is a “manifest necessity” for doing so, or when the “ends of public justice would otherwise be defeated.” The Court cautioned that this power should be used “with the greatest caution, under urgent circumstances, and for very plain and obvious causes.”5Library of Congress. United States v. Perez, 22 U.S. 579 (1824)
A hung jury is the clearest example. When jurors genuinely cannot agree, the prosecution is almost always allowed to try the case again. The same goes for circumstances that plainly prevent the trial from continuing.6Constitution Annotated. Amdt5.3.4 Re-Prosecution After Mistrial
If the defense asked for the mistrial and the judge granted it, the defendant is generally assumed to have given up any double jeopardy objection to being retried. The Court treats that as a deliberate choice: the defendant preferred a fresh start over a tainted proceeding.6Constitution Annotated. Amdt5.3.4 Re-Prosecution After Mistrial
There is one narrow exception. In Oregon v. Kennedy, the Supreme Court held that if the prosecution intentionally goaded the defendant into asking for a mistrial, double jeopardy bars a retrial. The key word is “intended.” Reckless, sloppy, or even winning-focused prosecutorial misconduct does not count. Only conduct specifically designed to provoke a mistrial motion qualifies, and defendants rarely manage to prove it.7Justia Law. Oregon v. Kennedy, 456 U.S. 667 (1982) A few states offer broader protection, blocking retrial for egregious prosecutorial misconduct even without proof of intent to provoke.
What a Mistrial Costs the Defendant
A mistrial is expensive for everyone, but the burden falls hardest on the defendant. No legal mechanism requires courts to reimburse a defendant’s legal fees after a mistrial, no matter who caused it. Someone who paid tens of thousands of dollars for private counsel the first time around may run out of money and have to rely on a public defender for the retrial. The prosecution draws from government resources that do not deplete the same way.
The emotional toll stacks on top. The Supreme Court has acknowledged that even when retrial is constitutionally permitted, a second prosecution “increases the financial and emotional burden on the accused, prolongs the period in which he is stigmatized by an unresolved accusation of wrongdoing, and may even enhance the risk that an innocent defendant may be convicted.”6Constitution Annotated. Amdt5.3.4 Re-Prosecution After Mistrial That is why the manifest necessity standard exists at all: the government should get one fair shot, not unlimited chances to wear a defendant down.