In most criminal prosecutions in the US, a defendant has an absolute right to have his or her case decided by a jury of his or her peers. The right, however, may be exercised by the defendant or waived. There are a number of reasons why defendants may choose to waive their right to jury trials, but the most common reasons are the expense involved, the risks involved if the defendant loses, and the option to accept a favorable plea agreement in lieu of a trial.
Jury trials can be expensive for both the state and for the defendant. The cost of bringing a jury pool in for voir dire, the time involved in selecting the jury members, and the extra expense of expert witnesses needed for jury trials can add up quickly for the state. A defense attorney will also charge the defendant accordingly, meaning jury trials are more expensive for the defendant as well. If a trial is inevitable, both sides may agree to waive the jury trial in favor a trial in front of a judge, or bench trial. A bench trial allows both sides to present and argue their case to a judge instead of a jury, thereby reducing the costs.
Risk is another important factor for defendants when they are deciding whether to waive jury trials. A jury is made up of randomly selected members of the community. Although they are instructed about the law, they have not studied it as a judge has, and therefore a jury often bases its verdict on evidence that one side or the other felt was unimportant or insubstantial. Jury trials are a gamble for defendants — they usually win big or lose big. Winning means an acquittal and the defendant goes free, while losing typically means a much harsher sentence then was offered through plea negotiations prior to trial.
In most cases, a defendant will be offered a plea bargain prior to the case proceeding to trial. A plea bargain allows the defendant to plead guilty to all or some of the charges in return for a predetermined sentence that is usually significantly less than the defendant would face at a trial. The benefit to the state of offering plea bargains is that they avoid the risk of acquittals and the expense of jury trials. The defendant also avoids the risk of conviction at trial and incurring a much more lengthy or serious sentence as a result.