When you contact law enforcement by calling 911 or a local agency, a police report is always logged. After officers respond to the scene of a reported crime, the officer is able to arrest a person on charges if probable cause exists, whether or not the victim agrees to move forward with a complaint.
After you file a report with the police department, the decision to press charges is often out of your hands. The government, either a local, state or federal branch, brings charges against an individual based on your report and decides which charges will go forward. In many instances, this allows law enforcement to protect domestic violence and other crime victims who may experience trepidation about moving forward with a case and feel threatened to drop a complaint.
TL;DR (Too Long; Didn't Read)
After police respond to the scene of a potential crime or a call, the officer makes the final decision about whether or not probable cause for an arrest exists.
Calls to Police
When you call 911 or a local law enforcement agency to report a crime or suspicious activity, a report is automatically created regarding your complaint. While this is not a full, formal police report, it is a public record. The reason for your call dictates what will happen when officers respond. If you call to report a suspicion that a crime is being committed against your property, such as burglary or vandalism, officers will arrive at your location and ask you questions to determine if there is probable cause that a crime occurred.
Proceeding with charges is at the discretion of the agency if the officer finds enough evidence to support an arrest. In some instances, such as a case in which a suspect is located on a burglary or theft call, officers may ask you to determine if the person had permission to be on your property or to access a vehicle or your home. Your answer here may help determine whether charges go forward. Always tell the truth, but indicate to the officer whether you want to pursue charges at this point. Even though an arrest may happen, prosecutors can take your request into consideration and drop the charges later or reduce them to a lesser offense, such as reducing a burglary charge without theft to trespassing.
Prosecution by the Government
After an arrest takes place, the case moves from the law enforcement agency to a city court, a district attorney's office, a state attorney or a U.S. Attorney. Attorneys at the agency review the case file, including the police report, to determine if a solid case exists. At this point, they will either drop the charges or take the suspect to court. If you feel strongly that a person should not go to jail following a complaint you made, contact the prosecuting body to express your feelings. Prosecutors often take the concerns of victims into account when determining which charges to pursue or planning plea arrangements.
Preventing crime victims from dropping charges offers an additional level of protection for the victim, of course. Victims of domestic violence or sexual assault often face pressure to "drop the charges" against the suspect. By removing the ability of a victim to stop a case from moving forward, prosecutors are able to secure convictions against violent offenders. This protection also starts from the time law enforcement is called to the scene of a domestic situation. If officers see evidence that an assault occurred, the officer can move forward with an arrest even if the victim provides no further statements.