A defendant has a constitutional right to a "speedy trial." The meaning of "speedy," and the benefits of demanding a "speedy trial," vary from state to state. In some states, most defendants have to waive their right to a "speedy trial" in order to get sufficient time to prepare their defenses. If a defendant demands a "speedy trial," he cannot later claim that he did not have time to prepare his defense. However, if a defendant demands a "speedy trial" and the prosecutor is not prepared to proceed to trial, the charges against the defendant may be dismissed.
A case that goes to trial will be heard by a judge in a "bench trial," or by a judge and jury in a "jury trial." In a jury trial, the judge decides the law, while the jury decides the facts. In a bench trial, the judge decides both the law and the facts. Both the prosecutor and the defendant have the right to demand a jury trial, although prosecutors are usually happy to consent to bench trials.
If a case is scheduled for jury trial, the parties engage in "jury selection." During jury selection, a panel of jurors is questioned by the judge, by the attorneys, or both, in a process called "voir dire." The purpose of this hearing is to determine if the jurors will be fair and impartial, and will decide the case based upon the evidence presented in court. Both the prosecution and defense can challenge jurors "for cause," claiming that the jurors are prejudiced against their side. The judge determines if there is valid cause to exclude a particular juror from hearing a case. Both the prosecution and defense also receive a limited number of "peremptory challenges," which allow them to remove jurors without any reason or explanation.
Typically, at the start of a trial the jury will be given preliminary instructions. The jury is instructed at this time that the defendant is presumed innocent, and that the presumption of innocence does not change until the jury begins deliberations. Jurors are not supposed to abandon the presumption of innocence before hearing all of the evidence in the case.
Next, the attorneys will present opening statements. Witnesses are presented first by the prosecution, and next by the defense. At times, the defense will not present any witnesses, either because the prosecution called all of the relevant witnesses during its case, or because the defense wishes to argue that the prosecutor's case is insufficient to justify conviction. The defendant cannot be compelled to testify against himself, but he has the right to testify in his own defense if he chooses to do so.
At the conclusion of the defendant's case, the prosecutor may present "rebuttal" witnesses to respond to arguments or evidence introduced by the defendant. Sometimes, the defendant will be allowed to present "rebuttal" to the prosecutor's "rebuttal."
After all of the testimony has been taken, the attorneys will present their closing arguments. The jury is then given additional instructions, and commenced deliberations. Sometimes the defense attorney will request a "directed verdict" of not guilty, meaning that the judge will instruct the jury that the only verdict it can return is "not guilty." These motions are commonly made, but are rarely granted. If the jury cannot reach a verdict, the judge will eventually discharge the jury. The prosecutor must then decide whether to dismiss the charges or to seek a new trial.
If the jury acquits the defendant, finding him not guilty, the case is usually over. (In the United States, the prosecutor cannot appeal an acquittal. However, in some other nations, the prosecutor has a limited right to appeal.)
A jury can also return a verdict of guilty. If a defendant is charged with more than one offense, the jury may convict the defendant of some charges while acquitting of others. At times, the jury will choose between related offenses. For some offenses charged, the jury may convict of a "lesser included" offense. For example, if a defendant is charged with "open murder," the jury may convict him for first degree murder, second degree murder, voluntary manslaughter, involuntary manslaughter, or negligent homicide. (Please note that the names and elements of the various homicide offenses may vary from state to state.)
After being convicted, a defendant may file post-trial motions, such as a motion for a new trial. These motions are rarely granted. The defendant may also file an appeal.