Mistrials are trials before a judge or jury that the judge has permanently halted mid-trial. The most common source of a mistrial is the jury’s failure to return a unanimous verdict (a situation known as a hung jury). Another example is when an attorney or a witness makes prejudicial statements that can't be corrected even by telling the jurors to disregard the statements. Serious misconduct by a party will also warrant a mistrial. Judges may also declare a mistrial upon learning that jurors have researched the case on their own on the Internet.

For an in-depth discussion of retrials following a successful motion for a mistrial, see Retrials in Criminal Cases.

Mistrial Procedure

Either side in a criminal case may move for a mistrial, and the court itself may declare one on its own. The process varies, depending on the reason for the mistrial.

• Hung jury. If the court is convinced that the jury cannot come to a unanimous decision, even with gentle urging from the judge and the assurance that they are doing as good a job as any jury would, the judge will declare a mistrial. The defense and prosecution will have to live with the judge’s decision, and the case will either be retried, settled (plea-bargained), or dismissed.
• Prosecutorial misconduct. Now and then, prosecutors will cross the line with respect to proper trial tactics, by deliberately introducing inadmissible evidence or purposefully asking improper questions that are designed to put information before the jury that the jury should not hear. When this happens, defendants often ask for a mistrial, fearing that the jury has been permanently tainted. If the judge feels that the behavior was extreme and the jury cannot be successfully admonished to disregard the incident, the judge will declare a mistrial. Most of the time, the case will be tried again, settled, or dismissed. (See the aforementioned article for the effect of the Double Jeopardy Clause of the U.S. Constitution in this situation.)
• Manifest necessity. Sometimes, circumstances beyond the control of the court must result in a mistrial. For example, the death of the presiding judge will result in a mistrial. Again, the case can be retried.

Questions for Your Attorney

• Can the prosecution move for a mistrial based on defense counsel misbehavior?
• What happens if the prosecutor deliberately creates the situation that gives rise to the mistrial?
• Will a judge grant a motion for a mistrial after the case has gone to the jury, but before a verdict has been announced?