Quick Answer: A mistrial is a judge’s ruling that ends a trial before it reaches a valid verdict, because something has made it impossible or unfair to continue. The most common cause is a hung jury, where jurors cannot reach the unanimous decision required to convict or acquit, even after extended deliberation. A mistrial is not an acquittal and does not mean the defendant is found innocent; it simply means the trial itself is voided. In most cases, especially when the mistrial results from a hung jury, the Double Jeopardy Clause of the Fifth Amendment does not prevent prosecutors from retrying the case before a new jury. Roughly 5% to 6% of U.S. criminal jury trials end in a hung jury and resulting mistrial, though the rate runs higher in complex, high-profile, or emotionally charged cases like murder trials.
In This Guide
- What a Mistrial Actually Means
- Hung Jury vs. Mistrial: What’s the Difference
- Common Causes of a Mistrial
- The “Manifest Necessity” Standard
- Does Double Jeopardy Prevent a Retrial?
- What Happens After a Mistrial
- Recent High-Profile Mistrials
- How Common Are Mistrials?
- Why Juries Have to Be Unanimous
- Frequently Asked Questions
What a Mistrial Actually Means
A mistrial is the court’s way of saying a trial cannot legally or fairly reach a verdict, so it has to stop. The judge ends the proceeding without a final decision from the jury, and legally, the trial is treated as if it never happened for purposes of a future prosecution. That’s an important distinction from a verdict: a mistrial isn’t a ruling on guilt or innocence at all. It’s a procedural reset.
This is different from an acquittal, which is a unanimous “not guilty” verdict that permanently ends the case and bars any retrial under the Constitution’s double jeopardy protections. A mistrial leaves the underlying question of guilt entirely unresolved, which is exactly why prosecutors are usually free to try the case again.
Hung Jury vs. Mistrial: What’s the Difference
These two terms get used interchangeably in casual conversation, but they describe different things. A hung jury, also called a deadlocked jury, is a jury that cannot reach the unanimous verdict required to convict or acquit, even after extended deliberation. The mistrial is the judge’s formal ruling that ends the trial because of that deadlock.
In other words: the hung jury is the cause, and the mistrial is the result. A hung jury almost always leads to a mistrial, but a mistrial can happen for many other reasons that have nothing to do with jury deadlock, which is why the two terms aren’t perfect synonyms even though they’re closely linked.
Common Causes of a Mistrial
While a hung jury is the most frequent cause, judges can declare a mistrial for a range of other reasons, including:
- Juror misconduct: A juror discussing the case outside deliberations, researching it online, or otherwise violating the judge’s instructions. Courts take this seriously because it threatens the core requirement that jurors decide a case based only on evidence presented in the courtroom.
- Prejudicial statements: An attorney or witness making a statement so damaging to a fair trial that even instructing the jury to disregard it can’t undo the harm. Courts sometimes describe this as being unable to “unring the bell” once jurors have heard something highly prejudicial.
- Prosecutorial or defense misconduct: Improper comments, mishandled evidence, or other significant procedural errors that make continuing the trial fundamentally unfair. This can include a prosecutor incorrectly attributing a statement to a defendant or introducing evidence a judge has explicitly ruled inadmissible.
- Emergencies affecting the court: The death or serious illness of the presiding judge, or enough jurors becoming unable to continue that the panel falls below the legally required number. Courts generally maintain a small number of alternate jurors specifically to guard against this, but a mistrial becomes necessary if too many jurors are lost.
- Defendant or witness health crises: A medical or mental health emergency during trial that makes it impossible to continue fairly, whether that involves the defendant, a key witness, or another essential participant in the proceeding.
The specific reason a mistrial is declared matters enormously, because it determines whether the case can be retried and whether double jeopardy protections apply. A mistrial triggered by an honest, unavoidable emergency is treated very differently under the law than one triggered by a party’s own misconduct.
The “Manifest Necessity” Standard
Courts use a legal standard called “manifest necessity” to decide whether ending a trial early, and potentially allowing a retrial, is justified. This doctrine traces back to the 1824 Supreme Court case United States v. Perez, which held that a judge can declare a mistrial and permit a retrial when there’s a genuine necessity to protect the interests of justice, even without the defendant’s consent.
A hung jury is the textbook example of manifest necessity. Because a deadlocked jury hasn’t reached any decision on the merits of the case, courts have long held that society’s interest in fair law enforcement outweighs a defendant’s interest in permanently ending the case without a verdict. That’s the legal foundation that allows prosecutors to retry a defendant after a hung jury without running afoul of the Constitution.
Does Double Jeopardy Prevent a Retrial?
This is the question most people are actually asking when they search “what does a mistrial mean.” The short answer: usually, no. The Fifth Amendment’s Double Jeopardy Clause protects people from being tried twice for the same offense, but that protection generally doesn’t apply after a mistrial caused by a hung jury, since no final verdict was ever reached.
The rules shift depending on how and why the mistrial happened:
- Hung jury mistrial: Retrial is almost always allowed. Jeopardy hasn’t “terminated” because no verdict was reached, and the deadlock is treated as manifest necessity.
- Mistrial requested by the defense: Also generally allows retrial, since the defendant chose to end the proceeding rather than let it continue.
- Mistrial caused by prosecutorial misconduct intended to provoke a mistrial: This is the major exception. If a prosecutor deliberately triggers a mistrial to get a more favorable jury or avoid a likely acquittal, double jeopardy can bar a retrial entirely.
Exact procedural rules vary somewhat by state and by federal versus state court, but this framework holds across nearly every U.S. jurisdiction: a mistrial is a non-ending, not a final resolution, and only specific forms of prosecutorial bad faith close the door on trying again.
What Happens After a Mistrial
Before a judge formally declares a mistrial over jury deadlock, there’s usually an intermediate step. If a jury reports it can’t reach a verdict, the judge will often give what’s known as an Allen charge, an instruction encouraging jurors to keep deliberating and reconsider their positions in light of the majority’s views, without abandoning their own honest judgment. Only after the jury reports back that further deliberation would be futile does the judge typically declare a formal mistrial and discharge the jury. This step matters procedurally, since the formal declaration on the record establishes the legal basis for what can happen next.
A mistrial doesn’t automatically end a case, and it doesn’t mean a defendant is released or the charges disappear. Once a mistrial is declared, several outcomes are possible:
- Retrial: The prosecution decides whether to try the case again before a new jury. This is common, especially for serious charges, though it requires committing significant time and resources to a second trial, and retrial conviction rates vary considerably by case.
- Plea agreement: Rather than retrying the case, prosecutors and the defense may negotiate a plea deal, particularly if the first trial revealed weaknesses in either side’s case or if a split verdict on the initial jury note hinted at how a future jury might lean.
- Dismissal: Prosecutors can choose to drop the charges entirely, especially if they conclude the evidence isn’t strong enough to secure a conviction in a second trial, or if the resources required for a retrial aren’t proportionate to the likely outcome.
In the meantime, a defendant is not automatically freed. Depending on the charges and the terms of any prior bail or custody arrangement, they may remain in custody, under state supervision, or on bail while prosecutors decide how to proceed. A status hearing is typically scheduled fairly quickly after a mistrial to determine next steps, and the prosecution isn’t always required to announce its decision on retrial immediately.
Recent High-Profile Mistrials
A handful of closely watched U.S. criminal trials in recent years illustrate how this process plays out. In one widely covered case, a Massachusetts jury deliberating for several days in a murder trial told the judge it was hopelessly deadlocked, split 11 to 1, prompting the judge to declare a mistrial after an emergency appeal from the defense was denied. Prosecutors in that case have not yet announced whether they’ll seek a retrial.
In another closely followed case, a Massachusetts trial involving a woman accused of killing her police officer boyfriend ended in a mistrial after the jury deadlocked. Because a hung-jury mistrial isn’t an acquittal, prosecutors were free to retry the case, and the second trial did reach a verdict, illustrating the full arc: deadlock, mistrial, retrial, and finally a binding outcome that double jeopardy then makes permanent.
These cases share a common thread: both involved serious charges, extensive media coverage, and jury deliberations that stretched well beyond what’s typical, factors researchers consistently link to higher rates of jury deadlock.
How Common Are Mistrials?
Despite how frequently mistrials make headlines in high-profile cases, they’re statistically uncommon across the criminal justice system as a whole. Research compiled by the National Center for State Courts found an average hung jury rate of about 6.2% across state courts, with substantial variation between jurisdictions. Other studies put the national rate closer to 5% to 6%, or as low as 2% to 3% depending on methodology and time period studied.
Murder trials and other serious felony cases tend to hang at higher rates than the average. Researchers point to a few consistent factors: complex or conflicting forensic and testimonial evidence, which one analysis linked to roughly 71% of jury deadlocks, and the emotional intensity that comes with cases involving child victims, domestic violence, or graphic details, all of which can make it genuinely harder for twelve people to reach unanimous agreement. It’s also worth remembering that only a small fraction of criminal cases ever reach a jury trial in the first place: most are resolved through plea agreements long before a jury is ever seated, meaning the cases that do go to trial, and hang, tend to be the ones where the evidence or stakes are least clear-cut.
Why Juries Have to Be Unanimous in the First Place
Part of what makes hung juries possible at all is the unanimity requirement itself. In federal criminal trials and in the overwhelming majority of states, a jury must agree unanimously to convict or acquit; a single holdout juror, out of twelve, is enough to produce a deadlock. That requirement is rooted in the idea that a criminal conviction, given the severity of what’s at stake, should reflect genuine, complete agreement rather than a simple majority.
A small number of states historically allowed non-unanimous verdicts in certain cases, most notably Oregon and Louisiana, but that landscape has shifted. The U.S. Supreme Court’s 2020 decision in Ramos v. Louisiana held that the Sixth Amendment requires unanimous jury verdicts in state criminal trials for serious offenses, effectively ending non-unanimous verdict practices nationwide going forward. That ruling means the potential for a hung jury, and the resulting possibility of a mistrial, now applies uniformly across all fifty states in serious criminal cases, whereas a small number of jurisdictions had previously been able to reach a binding verdict even with one or two dissenting jurors.
Frequently Asked Questions
What does it mean when a judge declares a mistrial?
It means the judge has ended the trial before reaching a valid verdict because continuing would be impossible or fundamentally unfair. The trial is voided; it does not count as a conviction, an acquittal, or any finding on guilt.
Is a mistrial the same as an acquittal?
No. An acquittal is a unanimous “not guilty” verdict that permanently ends the case. A mistrial leaves the question of guilt unresolved and generally allows the case to be retried.
Can someone be retried after a mistrial?
In most cases, yes. Double jeopardy typically does not bar a retrial when the mistrial resulted from a hung jury or was requested by the defense, since no final verdict was reached. The main exception is when a prosecutor deliberately causes a mistrial to gain an unfair advantage.
What is a hung jury?
A hung jury, or deadlocked jury, is a jury that cannot reach the required unanimous verdict after extended deliberation. It is the most common cause of a mistrial, though a hung jury and a mistrial are not technically the same thing; the hung jury is the cause, and the mistrial is the judge’s resulting order.
Does a mistrial mean the defendant is released from jail?
Not automatically. A mistrial voids the trial, not the underlying charges. Depending on the case, the defendant may remain in custody, under state supervision, or on bail while prosecutors decide whether to retry, offer a plea, or dismiss the case.
How often do trials end in a mistrial?
Hung juries, the leading cause of mistrials, occur in roughly 5% to 6% of criminal jury trials nationally, according to state court research, though rates vary by jurisdiction and tend to run higher in serious, complex, or emotionally intense cases like murder trials.
What happens if prosecutors decide not to retry a case after a mistrial?
They can formally dismiss the charges, which ends the case, or negotiate a plea agreement with the defense instead of going through a second trial. The decision often depends on how strong the original evidence appeared and how resource-intensive a retrial would be.
Do all states require a unanimous jury verdict?
Yes, as of the Supreme Court’s 2020 ruling in Ramos v. Louisiana, all states must require unanimous jury verdicts for serious criminal offenses. A small number of states, including Oregon and Louisiana, previously allowed non-unanimous verdicts in some cases before that decision.
What is an Allen charge?
It’s a jury instruction a judge gives when a jury reports it’s deadlocked, encouraging jurors to continue deliberating and reconsider their positions in light of other jurors’ views, without abandoning their own honest conclusions. Judges typically use it before declaring a formal mistrial, to give the jury one more chance to reach a verdict.
Bottom Line
A mistrial is a procedural stop, not a verdict. It most often happens when a jury cannot reach unanimous agreement, and it generally leaves prosecutors free to retry the case, negotiate a plea, or drop the charges rather than closing the book on guilt or innocence either way. While mistrials draw outsized attention when they happen in high-profile cases, they remain statistically rare, affecting a small single-digit percentage of the criminal trials that make it in front of a jury in the first place. Understanding the difference between a mistrial and an acquittal, and knowing that double jeopardy usually doesn’t block a second attempt, helps make sense of why a case that ends in a deadlocked jury is often far from actually over.