When thinking about getting charges dismissed, we tend to think of a dismissal before trial or before a plea agreement. Charges also can be dismissed even if the case has gone to trial and the defendant has lost. A convicted defendant who wins an appeal can sometimes secure an order from the appellate court that the lower court (the trial court) dismiss the case or enter a judgment of acquittal rather than retry the case. A prosecutor also might decide to dismiss a case voluntarily after losing an appeal.
For information on how cases can be dismissed before trial, see Getting a Criminal Case Dismissed.
An appellate court might dismiss a case after it has reversed the conviction on the grounds of a bad search or arrest. After the appellate court rules that a search or arrest was improper, the court usually also will order that evidence resulting from the search or arrest cannot be introduced at trial. The appellate court may examine what's left of the case without the evidence from the search or arrest and determine that the prosecution does not have enough evidence to warrant another trial and order the lower court to dismiss.
In another scenario, if a case is overturned based on insufficient evidence to support the defendant's arrest (and no other evidence suggests that the defendant would have been arrested for this crime under other circumstances), the court may conclude that there is no remaining evidence to tie the defendant to the crime. Even if the appellate court does not order a dismissal, the prosecutor may decide there is not enough evidence to secure a conviction.
Similarly, if the appellate court rules that a search was unconstitutional, and further rules that the evidence resulting from the search may not be considered, the prosecution may be left without enough evidence to support a finding of guilt on the charge. In this instance, again, the appellate court may order dismissal or the prosecutor may decide he has no choice but to dismiss the charges.
Occasionally, an appellate court will reverse a finding of guilt on the grounds that the jury did not have enough evidence to support its conclusion. Usually, the defense will have asked the trial judge to enter a judgment of acquittal, before the case went to the jury, and the trial judge will have denied that motion. On appeal, the defendant essentially makes the same argument – that the judge should have entered a judgment of acquittal before the jury started deliberations. In the rare case where the appellate court agrees with the defendant, the appellate court will reverse the conviction and direct the trial judge to enter a judgment of acquittal.
A court can hear only those cases in which the court has jurisdiction. Jurisdiction is the power and authority to hear a case and is given to courts by legislators (statutes) and the constitution. Now and then, a court oversteps its bounds and hears a case that it does not have jurisdiction to hear.
For example, federal courts can try cases that arise on federal property, but not state property. Imagine a robbery occurs on land that the federal trial court thinks the federal government owns. If the appellate disagrees with the lower court's analysis and concludes that the land is state owned, the appellate court would overturn the conviction for lack of jurisdiction (leaving the state free to charge the offense in state court). A trial in state court would not involve a violation of double jeopardy (the defendant could not argue that he was being tried twice for the same crime), because the federal and state courts are different sovereigns. (For more information on double jeopardy, see The Prohibition Against Double Jeopardy.)
If you have been charged with a crime, of course you don't want to bank on winning on appeal if you have not even gone to trial. Contact an attorney as soon as you learn of any criminal charges. A competent attorney will know your rights and can advise you on the options you have and decisions you will need to make.