To be successful, prosecutors must have the cooperation of the police, judges, victims, and witnesses. These actors in criminal justice, in turn, depend on prosecutors.
If a prosecutor doesn't have the cooperation of the police, he or she will encounter problems in investigating and in presenting evidence in court. Police depend on prosecutors almost as much as prosecutors depend on them. By sending cases back for further investigation and refusing to approve arrest warrants, prosecutors influence the police.
Police depend on prosecutors to advise them about legal issues in criminal cases and to train police officers in securing warrants, making legal arrests, and interrogating suspects. This interdependence creates a unique problem for prosecutors, who sometimes find themselves forced to either press charges against police officers for brutality or perjury—which will impair cooperation—or condone or cover up police crime—which is unethical.
Victims and witnesses
Many prosecutors prefer not to press charges if the main victim is unwilling to cooperate. Prosecutors' willingness to prosecute is sometimes based on their evaluation of a victim's role in the victimization and the victim's credibility as a witness. If the victim precipitated the crime through actions or words, the prosecutor will be less likely to press charges. If the victim has a criminal record, the prosecutor may not proceed with a case because a jury might not regard an ex‐con as a credible witness. For their part, victims and witnesses also need prosecutors. Unless the prosecutor takes a case forward, the victim has no chance to receive restitution or get revenge. In certain types of cases, such as those involving organized‐crime groups, witnesses need protection in order to stay alive to testify in court. The U.S. Marshals Service operates the Witness Security Program, which provides witnesses with new identities and security.
Judges and courts
Prosecutors must try to “read” judges. They need to predict what kind of sentence a judge is likely to mete out in a certain type of case and whether or not a judge will accept a plea agreement. A prosecutor might decide to drop a case rather than try it before a judge who the prosecutor knows will impose a lenient sentence or might opt not to enter into plea negotiations if the judge assigned to the case can't be counted on to support a plea bargain in court. In the case of the infamous gangster Al Capone, U.S. Attorney George E.Q. Johnson suffered great professional embarrassment when a judge nixed a plea agreement under which Capone would plead guilty in exchange for a short prison sentence.