It is the police who respond and take action to any citizen’s complaint lodged. The police may also feel suspicious and in such case they investigate, take down statements from various important witnesses and based on the findings make ready a report. They can arrest people during the course of the investigation. They may alternatively (as is usually the case) complete the report and submit it to the prosecutor’s office for evaluation.

It will be the prosecutor who will be deciding whether or not criminal charges will be filed against any suspect named in the police report. The procedures for filing charges, however, vary among jurisdictions. There are some jurisdictions that give greater discretionary powers to the police in charging defendants with specific crimes while others are there that provide greater powers in this regard to the prosecutor.
After being stopped by the police the person concerned i.e. the defendant may be ticketed for a "civil infraction" or may be ticketed or arrested for a "misdemeanor" or perhaps even be arrested for a "felony" It can be that the police may be arresting a person while alongside recommending a specific charge, yet, criminal charges are usually chosen solely by the prosecutor's office.
The process of criminal justice begins with an alleged crime. The police investigate upon the allegation that the complainant makes. The police, in this case, act as the agent of the government. A complaint or an indictment- a formal charging document as brought by the grand jury is filed with a court in the appropriate jurisdiction. A prosecuting attorney represents the interests of the state. The interests of the defendant are represented by the defense attorney or by the defendant pro se i.e. the defendant acting as his/her own attorney. The process culminates with a jury trial regardless of local laws that may be followed by mandatory or discretionary appeals to higher courts. The criminal lawyer makes you aware of your rights with the police, your rights in the courtroom and your rights upon conviction. Article Source: http://EzineArticles.com/?expert=Somdev_Mukherjee.