Prosecutors may also be influenced by their own political ambitions. Most prosecutors are elected officials, and many of them view their position as a stepping-stone to higher office. Their decisions on charges are often, therefore, affected by public opinion or important support groups. For example, a prosecutor may file charges on every shoplifting case, no matter how weak, to curry favor with local store owners who want to get the word out that shoplifters will be prosecuted.

Finally, some decisions are influenced by the prosecutor's sense of what justice requires in the case before him. Prosecutors are supposed to both enforce the law and "do justice." Doing justice means that occasionally a prosecutor decides not to prosecute a case (or files less severe charges) because the interests of justice require it, even if the facts of the case might support a conviction. For example, if an otherwise law-abiding person makes a one-time, foolish mistake, a prosecutor may decide that it would not serve any purpose to spend time and money prosecuting this person, especially when the chances that the person will re-offend are nil.

The Role of a Grand Jury

If a felony is involved, prosecutors sometimes leave it to grand juries to decide whether charges should be filed. Grand juries are similar to regular trial juries (called "petit juries") in that they are made up of randomly selected individuals. The grand jurors listen to evidence and decide whether charges should be brought against an individual (they decide whether to "indict" someone). However, unlike petit juries, which only sit on one case, grand juries involve a time commitment that typically lasts between 6 and 18 months. The grand jurors may address many cases in the course of their service. In addition, these crucial differences exist:

• Petit jurors decide whether defendants are guilty. Grand juries decide whether there is enough evidence to warrant a trial.
• Grand juries meet in secret proceedings. Petit juries serve during public trials.
• Grand juries have 15-23 people. By contrast, a petit jury usually consists of between 6 and 12 people.
• Petit juries generally have to be unanimous to convict a defendant. Grand juries need not be unanimous to indict. In the federal system, for example, an indictment may be returned if 12 or more jurors agree to indict.