In the federal system, prosecutors must generally persuade a grand jury that there is probable cause to indict a particular defendant with a specific crime.  This process is used in state cases as well, but there are more instances in which defendants are charged with crimes in state courts without being formally indicted.  In many cases, victims themselves may file an application for a statement of charges which will serve to initiate a criminal prosecution.  Though persons may charged with a crime in a criminal complaint, they may not be forced to stand trial unless the prosecutor preliminarily establishes probable cause to believe that the accused likely committed a crime.  Absent a grand jury indictment, this preliminary determination is made by a judge in a proceeding known as a preliminary hearing.

Unlike secretive grand jury proceedings, defendants and their lawyers may attend and participate in the questioning of witnesses called by the prosecution to testify at preliminary hearings.  Considering the fact that pretrial discovery is quite limited in most criminal cases, this provides defense counsel with a golden opportunity to ask tough questions that they might otherwise avoid in front of a jury at a later trial.  For example, in a rape case, defense counsel may wish to vigorously cross-examine the accuser in an effort to discredit her or emphasize inconsistencies in her account.  At trial, jurors may perceive such cross-examination as "badgering" the victim.  But, at a preliminary hearing where a single judge is given the limited task of deciding whether there is enough cause to go forward with a criminal case, the defense has little to lose by obtaining answers to these difficult questions well in advance of trial.