An arrest doesn't always mean criminal charges will be filed in a case. The intake prosecutor generally reviews a law enforcement officer's report and may decline to file charges for a number of reasons. Among the most common are:
The offense is trivial or low priority. Prosecution offices may view certain types of crimes as insignificant or not worth pursuing (perhaps due to limited resources or political pressures). For example, a prosecutor may decline to prosecute all cases involving possession of very small quantities of marijuana. Or the prosecutor may decide not to pursue charges against a group of protesters arrested at a local political rally.
Minor, nonviolent case goes to mediation. In some locations, minor criminal complaints are diverted out of the court system before prosecutors file charges. The alleged offender and complainant are brought together to discuss their problem, sometimes with a facilitator or mediator, to come up with some sort of solution. If you're interested, ask your defense attorney or public defender whether mediation is available in your jurisdiction.
Civil compromise. Defense lawyers often try to prevent the filing of criminal charges by arranging for a civil compromise. Much like mediated agreements, the defendant agrees to reimburse a victim for damages. In return, the victim asks a prosecutor not to file charges. This option gives wealthier arrestees a ticket out of the criminal justice system that may not be available to those who can't afford it.
The police officer failed to observe the suspect's rights. If, through obvious police error, the prosecution lacks enough admissible evidence to make a criminal charge stick, the charge probably won't be brought in the first place.
The victim asks that no charges be brought. Charging decisions are for prosecutors, not victims. However, if victims ask prosecutors not to bring charges and make it perfectly clear that they will not cooperate, prosecutors often won't file charges. In past years, this type of situation was common in family disputes. In the heat of an argument, battering, or other abuse, the victim would call the police, leading to the arrest of the abuser. For personal reasons (whether fear of retaliation or hopes of making up), the victim would then refuse to cooperate and charges would not be filed. In recent years, the law enforcement community has begun to take domestic abuse allegations more seriously, and many prosecutors now bring and prosecute domestic abuse charges even if the victim doesn't want to pursue the case.
The prosecutor views the suspect as a good person. Occasionally, a prosecutor will decide that a basically good person made a stupid mistake that shouldn't result in a consequence as severe as a criminal charge. In such a situation, the prosecutor will refuse to prosecute, either in the interests of justice or because it would be a waste of resources (time and money) to charge such a person with a crime, even though the initial arrest was valid.
The prosecutor wants one defendant. Commonly, a prosecutor will drop charges against one suspect in exchange for that suspect's testimony against another suspect.
This article was excerpted from The Criminal Law Handbook, by Paul Bergman, J.D., and Sara J. Berman, J.D.