Learn how police officers and prosecutors initiate criminal cases.

How does a criminal case get started? Usually with a police arrest report. The prosecutor then decides what charges to file, if any. The case can then go to a grand jury for an indictment or to a preliminary hearing where a judge decides if there is enouogh evidence to proceed.  Here's how this all works. 

Arrest Reports and Criminal Charges

After an arrest, the arrest report is sent to a prosecutor, whose job it is to initiate and prosecute criminal cases. Arrest reports summarize the events leading up to arrests and provide numerous other details, such as dates, time, location, and weather conditions of the crime, and witnesses' names and addresses, if that information is available.

The prosecutor will either:

• decide that the case should be charged (as a felony or a misdemeanor), and file a complaint with the trial court
• decide that the case should be charged as a felony and bring evidence before citizens serving as grand jurors, who will decide what charges, if any, to file, or
• decide that the matter should not be pursued.

Prosecutors can file charges on all crimes for which the police arrested a suspect. Or, they can file charges that are more or less severe than the charges leveled by the police.

Charges Must Be Filed Quickly

For suspects who are in custody, speedy trial laws typically require prosecutors to file charges, if at all, within 72 hours of arrest. Some jurisdictions require prosecutors to charge a suspect even sooner. For example, California requires that charges be filed within 48 hours.

However, prosecutors' initial charges are subject to change. For example, a prosecutor may not make a final decision on what charges to file until after a preliminary hearing, which may take place more than a month after arrest.

How a Prosecutor Decides Whether to File Charges

A prosecutor's decision to file charges may be influenced by factors beyond the specific facts of the incident described in the police report.

Policies on certain crimes. Some prosecution offices adopt policies on certain types of crimes, often in response to community pressure, and these policies may dictate the prosecutor's approach in any given case. For example, an office may decide that arrests for driving under the influence of drugs or alcohol will always be taken to trial and not "plea bargained" down to a lesser offense.

Political ambition. 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 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.

What justice requires. Finally, some decisions are influenced by the prosecutor's sense of what justice requires in the case before her. Prosecutors are supposed to both enforce the law and "do justice." Doing justice means that a prosecutor occasionally 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 (that is, 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.